﻿308 R. Etheridge, Jun. — Contributions to Palceontology. 



Genus Psammodus, Agassiz. 

 Psammodus rugosiis, Agassiz. Plate XIIL Figs. 7-9. 



P. riigosus, Ag. ; Rech. Poissons Foss. vol. iii. (1833-34), p. Ill, Atlas iii. t. 12, f. 



14-18, t. 19, f. 15. 

 ,., „ M^Coy, Brit. Pal. Foss., p. 644. 



Tontli. — Oblong, lingual ; length, without the lateral prolongation, 

 2 inches 5 lines; breadth 1 inch 2 lines; height 8 lines. The longer 

 margins of the crown are convex and rounded, with sharp edges, 

 and bound the somewhat concave centre of the crown, which is 

 higher in the middle than at the shorter ends. One of the shorter 

 margins (the anterior ?) is obliquely convex, and its edge roughly 

 crenulated ; the other (or posterior?) is somewhat concave or ex- 

 cavated, with the edge a little bevelled outwards and deeply slit 

 vertically. Sides. — The longer sides are more or less vertical, or 

 at right angles to the crown ; one of the shorter sides (the anterior?) 

 is bevelled inwards for the articulation of the preceding tooth ; the 

 other shorter side is like the longer lateral ones, almost vertical, 

 and is extended backwards with one of the latter to form a pointed, 

 laterally compressed prolongation. Ornamentation. — The crown is 

 covered with minute, vermiform, transverse, tortuous fringed ridges, 

 many of which bifurcate, and become more broken up on the longer 

 lateral margins. The longer lateral sides are roughened. 



Obs. — The present tooth differs from Agassiz's typical figures in 

 the absence of the prominent rounded eminence on the posterior 

 part of the crown, although one of his specimens appears to have 

 been devoid of it. Agassiz considered that an intimate affinity 

 existed between the teeth he named P. porostis and P. rugosus, whilst 

 M'Coy united the two under the one name P. rugosus.^ The latter, 

 in his description, says, that the long sides are either parallel, or 

 one is concave and the other convex, and usually bevelled obliquely 

 on the under-side for articulation, the short lateral sides on the other 

 hand being rudely vertical. He further adds that the surface of 

 the crown is raised towards the short sides, which are usually the 

 most prominent parts of the tooth. It will be observed that the 

 specimen now figured does not quite correspond with this descrip- 

 tion, as the long lateral sides are quite vertical, and one of the short 

 sides is bevelled; further, the surface of the crown towards the 

 shorter ends is in each case depressed instead of being elevated or 

 prominent. The concave and convex shorter sides are probably 

 similar to those so described in P. canalicidatiis, M'Coy,- which is 

 considered by Messrs. Davies and Barkas as a synonym of P. 

 rugosus, Ag.^ Neither Agassiz nor M'Coy make any mention in 

 their descriptions of the single lateral prolongation seen in the 

 present tooth. 



Loc. and Horizon. — This fine example was communicated to me 

 by my friend Prof. H. A. Nicholson, M.D., who obtained it from the 

 highest limestone but one, in the Carboniferous Limestone series, 



1 Brit. Pal. Foss., p. 644. 



2 Brit. Pal. Foss., p. 643. 



3 Geol. Mag., 1874, Dec. II. Vol. I. p. 648. 



