NATRICINAE, Bonaparte, 1838

Myers, Charles W., 2011, A New Genus and New Tribe for Enicognathus melanauchen Jan, 1863, a Neglected South American Snake (Colubridae: Xenodontinae), with Taxonomic Notes on Some Dipsadinae, American Museum Novitates 2011 (3715), pp. 1-36 : 14-15

NATRICINAE

The great majority of these snakes have strongly to weakly bilobed, spinose hemipenes that were recently thought to be always acalyculate (McDowell, 1961: 504–505; Rossman and Eberle, 1977: 38–41; Dowling and Duellman, “1974–1978” [1978]: 112d.1; Zaher, 1999: 25, 32–33). Cadle (MS.), however, has demonstrated the presence of calyces in Rhabdophis and further explored hemipenial diversity among natricines.

It is believed that in most natricine hemipenes the sulcus spermaticus either bifurcates with centripetal branches on the lobes, or else extends unforked straight (centrolineally) to a variable-sized median nude area in the middle of an unilobed or weakly bilobed head. 8 Other configurations, however, also occur and it is difficult to generalize.

6 The “left” and “right” hemipenial lobes and/or sulcus branches refer to the everted hemipenis as viewed looking toward its sulcate side (hemipenial lobes are dorsal and ventral when retracted). “Sinistral sulcus” and “dextral sulcus” are useful descriptors for unforked sulci extending either to the left or right lobe, respectively (Rossman and Eberle, 1977: 40).

7 Shwayat et al. (2009: 98, fig. 9A–D), however, describe four species of the colubrine genus Eirenis as each having a single sulcus that either “turns left” or “turns right,” or “turns left or right” in the same species. These conditions are not evident in their photographs, which are reproduced too small for clarity. When the PDF is greatly enlarged on a computer screen, however, the four unilobed organs all appear to have centrolineal sulci spermatici that seem to terminate in the middle of the hemipenial apices.

8 Zaher (1999: 26) suggested that the nude area derives from broadly-expanded centripetal branches of a forked sulcus, but this can be questioned. In Macropisthodon rudis a sinistral sulcus appears to extend to the tip of the left lobe before meeting a centripetal “nude apical groove” that also seems to be represented by a

“narrow nude pocket” on the medial side of the right lobe (Rossman and Eberle, 1977: 39–40, fig. 4C ). In some other natricines, the sulcus groove remains distinct within or even crosses the nude area (Cadle, MS.).

The right branch of the sulcus spermaticus has been lost in a several derived natricine genera, including Afronatrix and Hydraethiops , with the remaining left branch extending centripetally onto a small left lobe as in Amnesteophis . For illustrations of the everted hemipenis of Afronatrix anoscopus see Zaher (1999: fig. 18, upper); for the retracted and everted organs of Hydraethiops melanogaster see Bogert (1940: fig. 4A ) and Zaher (1999: fig. 18, lower), respectively. 9 These acalyculate, spinose hemipenes—with a nude area in the crotch—are similar to that of Amnesteophis ( fig. 5 ) except that the Amnesteophis organ bears distal flaplike papillae, which are absent or at least rare on natricine hemipenes. 10

Natricines (and few other colubrids) are characterized by presence of hypapophyses on the posterior vertebrae, but posterior hypapophyses are lacking in Amnesteophis . Furthermore, even small natricines tend to be relatively robust compared with the slender Amneseophis. Therefore, despite aforesaid hemipenial similarities with a few Old World natricines, the slender body, relatively narrow head, and lack of precaudal hypapophyses seem to preclude Amnesteophis from the Natricinae .

Figures

FIG. 4. Maxillary dentition of Amnesteophis melanauchen (Jan 1863). Right maxilla of holotype of Enicognathus melanauchen in lateral and ventral views (scale line = 1 mm).

FIG. 5. Hemipenis of Amnesteophis melanauchen (Jan 1863). Manually everted left organ of holotype of Enicognathus melanauchen, in sulcate (left), apical (top), and asulcate (right) views. (Basal half of organ is split and spread flat; the inflated distal half is fully everted but probably not maximally expanded.) The basally spinulate hemipenis is mostly spinose (spines emphasized by stippling); the spines are replaced on the small lobes by larger, soft flat- tened papillae; the unforked sulcus spermaticus extends centripetally to apex of the left lobe (sinistral sulcus) without entering a nude area in the lobular crotch; calyces are lacking (scale line = 1 mm).