308 R. Etkeridge, Jun. — Contributions to Palceontology. 
Genus Psammodus, Agassiz. 
Psammodus rugosus, Agassiz. Plate XIII. Figs. 7-9. 
P. rugosus, Ag. ; Rech. Poissons Poss. vol. iii. (1833-34), p. 111, Atlas iii. t. 12, f. 
14-18, t. 19, f. 15. 
,, ,, M‘Coy, Brit. Pal. Foss., p. 644. 
Tootli. — Oblong, lingual ; length, without the lateral Prolongation, 
2 inches 5 lines; breadth 1 inch 2 lines; keight 8 lines. The longer 
margins of the crown are convex and rounded, with sharp edges, 
and bound the somewkat 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 baekwards with one of the latter to fonn 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 affin ity 
existed between tbe teeth he named P. porosus and P. rugosus, wliilst 
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 oonvex, and usually bevelled obliquely 
on the under-side for articulation, the short lateral sides on the other 
hand being rudely vertical. He furtlier 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. canaliculatue, M‘Coy, 2 which is 
considered by Messrs. Davies and Barkas as a synonym of P. 
rugosus, Ag. 3 Xeither 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. 
3 Brit. Pal. Foss., p. 643. 
3 Geol. Mag., 1874, Dec. II. Vol. I. p. 548. 
