294 Mr. R. Etheridge, Jun., on the Gasteropoda 



are only Chiton-Tpl&tes ; but any attention to the muscular 

 scars as figured by Phillips, or described by De Koninck, 

 would have at once dispelled this idea. 



In Metoptoma oblonga the muscular scars possess identically 

 the same character as those of M. pileus, Phill., or M. Solaris, 

 De Kou., and, like them, are striated lengthways. 



Now, if we compare these scars in either of the three 

 species just mentioned with those of a recent Patella, we find 

 the resemblance complete, the impressions in the latter being 

 to all intents and purposes horseshoe-shaped, with the free ends 

 directed towards the anterior or narrowed portion of the 

 shell. Under these circumstances Metoptoma cannot be said 

 to differ from Patella in more than its truncated posterior end 

 and some other minor particulars. 



The form of the muscular impressions and the utter absence 

 of any facet-surface for rolling up, as in Chiton, the truncated 

 posterior side of Metoptoma being in no way analogous to this, 

 at once separate the latter from the former. In the Chitones 

 the facet or overlapping surface of the valves is differently 

 ornamented from their exposed surfaces, whilst in Metoptoma 

 the posterior truncated side is ornamented in a similar manner 

 to the rest of the surface. On the whole, Metoptoma may be 

 conveniently retained for shells of the Palaeozoic rocks having 

 the general appearance of Patella but with the posterior end 

 truncate. 



Pileopsis ? trilobus, Phillips (p. 224, t. 14. 

 figs. 12 & 13). 



Not in the Gilbertson collection. 



Pileopsis tubifer, Sowerby (Phillips, p. 224, 

 t. 14. fig. 14). 



This, in many respects a remarkable specimen, has not been 

 done justice to in Phillips's figure. The example preserved 

 in the Gilbertson collection, and used by Prof. Phillips, also 

 forms the actual type of the species, having been borrowed 

 and figured by Mr. J. de C. Sowerby. The shell is more or 

 less imbedded in limestone ; and there are visible two rows of 

 spine-bases, one on each side, with distinct traces of a central 

 third one. From the margin of the shell, in a .line with each 

 of these rows, a coarse irregularly formed spine projects, en- 

 closed to a great extent in matrix. The apex is not exposed ; 

 M'Coy says, however, it is arched, but not incurved, and that 

 the general form of the shell is here more lengthened and 

 narrower than in any species of this genus. 



P. tubifer, which is apparently any thing but common, has 



