Dromilites bucklandii (H. Milne Edwards, 1837a)

van Bakel, Barry W. M., Robin, Ninon, Charbonnier, Sylvain & Saward, Jeff, 2017, Revision of Dromilites bucklandii (Crustacea, Decapoda, Brachyura): Type material revealing its real identity, a junior synonym, and a new species, Palaeontologia Electronica 20 (3), pp. 1-12 : 3-5

Dromilites bucklandii (H. Milne Edwards, 1837a)

Figure 1 , Table, and Appendix

1837a Dromia bucklandii H. Milne Edwards ; H. Milne Edwards, p. 178–179.

1981 Dromilites simplex Quayle and Collins ; Quayle and Collins, p. 736–737, pl. 104, figs. 1-3, 10 (nov. syn.)

1991 Dromilites simplex Quayle and Collins ; Müller and Collins, p. 62.

2001 Dromilites simplex Quayle and Collins ; Guinot and Tavares, p. 531.

2006 Dromilites simplex Quayle and Collins ; Collins and Saward, p. 68, table 1.

2009 Dromilites simplex Quayle and Collins ; Rayner et al., p. 55.

2009 Dromilites simplex Quayle and Collins ; Van Bakel et al., p. 56.

2010 Dromilites simplex Quayle and Collins ; Schweitzer et al., p. 64.

2010 Dromilites simplex Quayle and Collins ; Schweitzer and Feldmann, p. 423–425, figs. 4-5.

2012 Dromilites simplex Quayle and Collins ; Schweitzer and Feldmann, p. 594.

2012 Dromilites simplex Quayle and Collins ; Quayle and Collins, p. 36, table 1–2.

2016 Dromilites simplex Quayle and Collins ; Artal et al., 2016, p. 443.

Type material. H. Milne Edwards (1837a) did not report if there was more than one specimen included in his type series. Only one syntype is housed in the palaeontological collections of the

MNHN, Paris, in H. Milne Edwards’ collection

(labeled “bucklandi ”, “Sheppey ( Angleterre)”,

“Eocène”, with a Milne-Edwards catalog number). We select this specimen MNHN.F.B21561 to be the lectotype (see Figure 1 a-1c).

Additional material examined. NHMUK PI IC 34026 (Spencer coll.) (male, London Clay, Highgate, London, 51°34'18.29"N / 0°9'0.82"W); NHMUK PI In. 28173 (Venables coll.) (London Clay, Bognor Regis, Sussex, 50°46'58.82"N / 0°40'23.00"W); NHMUK PI In. 61700 (Elmore Formation, Unit 7, Lee-on-the-Solent, Hampshire, 50°48'7.54"N / 1°12'8.47"W); NHMUK PI IC 548 (London Clay); MAB.k. 3590 ( Isle of Sheppey , foreshore exposure, Kent, United Kingdom, 51°20'36.77"N / 1°0'2.76"E), figured in Rayner et al., 2009, p. 55 (Isle of Sheppey foreshore exposure, Kent, United Kingdom) (see Table) .

Remarks on type specimens. H. Milne Edwards (1837a) described, but did not figure Dromia bucklandii . Bell (1858) was the first to use Milne Edwards’ species including it in Dromilites , and published a plate with figures of specimens currently held at the NHMUK (Wetherell coll.). His description is clearly based on these figured specimens. Specimens conspecific to Bell’s species have been referred to as D. bucklandii by all subsequent authors, such as Quayle and Collins (1981) and Schweitzer and Feldmann (2010). However, none of these authors have apparently examined the original type material of Milne Edwards. One syntype of D. bucklandii, MNHN.F.B 21561, is still housed in the MNHN collections (see Figure 1C ) and has never been figured or referred to in later works on the species. After careful examination, it appears that this specimen has a rather smooth carapace preserved with the cuticle with regions not strongly inflated or marked with strong tubercles. It is not conspecific to the material figured and described by Bell (1858), as further explained below. This means that Bell (1858) described and figured specimens that did not correspond to D. bucklandii (this has no influence on the type species designation of Dromilites , which is only a nomenclatural act, and Bell was the first to use the species for this genus). Quayle and Collins (1981) described D. simplex . They discussed (p. 737) that “the absence of marked tuberculation throughout these stages, together with weakly developed, non-bifurcated marginal spines and lack of transverse tubercles on the urogastric lobe immediately distinguishes this species from D. bucklandii . ” When comparing to D. bucklandii they obviously referred to the specimens figured and described by Bell (1858), but not to the type material of H. Milne Edwards. Now having examined both the type material of D. bucklandii and D. simplex , we can conclude that the latter is a junior synonym of D. bucklandii .

Description. Carapace subovate, length slightly exceeding width (holotype dimensions: CL= 21.5 mm, CW= 19.5 mm, FM= 7.5 mm, OFM= 14 mm, PM= 11.2 mm), maximum width at midlength, convex in longitudinal cross section, strongly convex in transverse cross section; orbitofrontal margin prominent, wide, 72% maximum carapace width. Rostrum projected beyond orbits, large, broadly triangular, bilobed, axially notched, frontal margin slightly convex; orbits forwardly, outwardly directed, upper orbital margin concave, outer orbital corner angular. Lateral margin angular in cross section; anterolateral margin weakly convex, with three strong teeth two anterior, one posterior to cervical notch; anterior two teeth pointed triangular; third lateral spine prominent, flattened anteriorly, outwardly directed, posteriorly forming flanged lateral margin with four to five granules. Posterolateral margin short, anteriorly straight, posteriorly strongly curved, anteriorly bearing single small forwardly directed tooth. Posterior margin slightly shorter than orbitofrontal margin, straight, rimmed. Carapace regions rather smooth, marked by acute, shallow grooves; small epigastric swellings closely spaced, separated by short sulcus, mesogastric region undefined anteriorly, posteriorly only at base, wide, without tubercles, indistinct median groove. Protogastric regions flat; hepatic region inclined. Metagastric region trapezoidal, wide anteriorly, posterior margin inverted V-shape, surface laterally with oblique line of four to five pits, medially with indistinct paired gastic pits. Urogastric region low, triangular, apex directed forwards. Cardiac region weakly inflated, diamond-shaped, apex pointed posteriorly, centrally bearing two horizontally lined low bumps, pitted; intestinal region large, flat. Branchial region large, subdivided by oblique postcervical, branchial grooves; epibranchial, mesobranchial regions weakly vaulted; metabranchial region large, weakly vaulted.

Cervical groove widely V-shaped, deep, distinct on medial carapace, interrupted at axis by gastric pits, faint laterally, weakly notching carapace margin; branchial grooves more horizontal than cervical groove, acute, distinctly notching lateral margin; post-cervical grooves shallow, indistinct, conspicuously short; branchiocardiac grooves deep, curved, posteriorly converging to intestinal region.

Carapace epicuticle with numerous evenly spaced setal pits, microgranules. Internal mold and its ornamentation unknown.

Range. London Clay, Ypresian, lower Eocene.

Occurrence. London and Hampshire basins.

Figures

FIGURE 1. Dromilites bucklandii H. Milne Edwards, 1937. 1. Lectotype MNHN.F.B21561: (London Clay, Isle of Sheppey, Kent, United Kingdom): 1a. carapace in dorsal view, 1b. carapace in frontal view, 1c. carapace coated with ammonium chloride in dorsal view, 2. Holotype NHMUK PI IC 34026 (London Clay, Highgate, London, UK; Spencer coll.) of Dromilites simplex, nov. syn. of D. bucklandii: 2a. colored dorsal view, 2b. black and white dorsal view. Scale bars equal 10 mm. Photographs: Lilian Cazes (1) and Barry van Bakel (2).