Laelaps incrassatus, Cope, 1876

Cope, E. D., 1876, On some extinct reptiles and batrachia from the Judith River and Fox Hills beds of Montana, Proceedings of the Academy of Natural Sciences of Philadelphia 28, pp. 340-359 : 341-343

Laelaps incrassatus , Cope,

Proceed. Acad. Nat. Sci.1876 Oct.

The dentary bone of this species, above alluded to, is of compressed form, and becomes thin and plate-like in its posterior portion. The latter is excavated on the inner side, where it is probably applied to the opercular and surangular bones, if they exist, and a large foramen is continued from the concavity into the remaining part of the dentary, as a tubular canal. Above the forainen there originates a groove which runs parallel to the inner alveolar border to the posterior edge of the symphysis. The latter is short, and scarcely distinguished from the other surfaces; the attachment of the rami was evidently ligamentous and more or less movable. The anterior alveolar portion of the ramus is produced, so that the symphysis slopes backwards below. The interior border of the dentary bone is gently concave behind its middle. It is throughout convex in the transverse direction.

The external alveolar wall is an inch higher than the internal. The inner portions of the septa are apparently subject to exfoliation and subdivision in connection with the renewal of the teeth as a groove which is continuous with the inner alveolar borders, cuts them off from the other interior surface of the dentary bone. The external face of the dentary is in general plane, but is variously excavated along its superior border. An inch below the latter there extends a series of large foramina, each one of which is situated opposite to an interalveolar septum. They are more numerous anteriorly,,a foramen being opposite each alveolus as well, and each foramen is connected with the border by a shallow groove. Similar foramina extend down the outer side of the symphyseal border, and along the inferior border of the dentary for two-thirds of its length. The same proportion of the external face is obsoletely rugose through the presence of delicate lines of growth. Such lines extend on the lower part of the interior face obliquely upwards and backwards.

There are alveolae for fifteen teeth in the dentary bone. Of these only the second, third, fourth, fifth, twelfth, and fifteenth contained teeth capable of functional use at the time the jaw was inclosed in the lacustrine mud. Suceessional teeth occupy the first, tenth, and twelfth, but no two teeth are in an identical stage of protrusion. The section of the crown from and including the fourth to the last is nearly equilaterally lenticular. Their surface is smooth.

Measurements.	M.
Length of entire dentary bone	. 525
Depth at posterior border of symphysis	. 110
“ " last tooth	. 192
“ to internal groove	. 060
“ “ ‘ i foramen	. 074
Length of crown of second tooth	. 029
anterio-posterior Diameter of second tooth at base {transverse	. 013. 018
Length of crown of twelfth tooth	. 043
anterio-posterior Diameter at base of twelfth tooth {transverse	.025. 017
Length of crown of superior?canine	062
Antero-posterior diameter of do.	. 028

As compared with the Laelaps aquilunguis , of which a portion of the dentary hone is known, this species difiers in the greater diameter of its interior border anteriorly y,in the presence of the internal groove, in the greater elevation of the external aiveolar wall, and, if the character be constant, in the greater robustness of the form of the dental crowns. The individual here described is rather larger than the type of L. aquilunguis , but it is probable that the species were not very difierent in dimensions.