1 N VERTEBRATE PALJ30NT0L0( IV. 28 i 



of the species of Siphonaria, though in the latter two characters they do not 

 differ from one section of that genus; but, in that section, the apex is mar- 

 ginal, and the muscular scars and other characters as in the other section. 

 Again, some of our specimens of the shells under consideration present such 

 appearances as to leave doubts whether there was really a complete break in 

 the muscular scar at the point of interruption. It is always abruptly attenu- 

 ated there, and apparently, in some cases (fig. 5, c, pi. 18), presents a com- 

 plete and wide gap. But, in other cases, it is broken into several spots, or in 

 still others, apparently represented by a continuous slender line at that point 

 as seen in fig. 4, a, of same plate ; which would seem to preclude the possi- 

 bility of the protrusion of a siphon there; while it is worthy of note that 

 none of the species show any traces of a siphonal groove. 



'Compared with Tecturn. Gadinia, and Scunia, these shells will be seen 

 to differ from them all in the partial or entire interruption of the muscular 

 scar already mentioned, as well as in the abruptly-reflexed point of the sum- 

 mit. In general appearance, some of the more elevated species nearly 

 resemble Scurria, but differ in the characters mentioned. 



In regard to the family-affinities of such fossil types, having no existing 

 species, it is of course very difficult to arrive at satisfactory conclusions If 

 the partial or entire break seen in the scar of the muscular attachment of 

 these shells was for the passage of a siphon, then the propriety of referring 

 them to the family SiphonariidcB, could scarcely admit of a doubt; but the 

 fact that in some instances, as already stated, the muscular scar does not seem 

 to be completely divided (though always much attenuated) on the right poste- 

 rior side, appears to indicate that there could hardly have been any such 

 organ protruded there. Consequently, although originally inclined to refer 

 the genus to the Siphonariidae, I was left in much doubt on this point, and 

 finally concluded to place it provisionally in the Acmaidoi (— Tecturidce). 

 Dr. Stoliczka, however, refers it to the Lepetidce ; and Mr. Dall, a much better 

 authority, with greater probability of correctness, thought, after a careful 

 examination of the type-specimens, that the group should go into the Sipho* 

 i, nn<U?: which conclusion I have here, at least provisionally, adopted. 



It is perhaps hardly necessary to add that if these shells really possessed 

 a natural perforation at the apex, as was at one time suspected might possibly 

 have been the case, they would not belong to any of the above-mentioned 



