268 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



thin, inner layer, having a broad notch, or sinus, on the dorsal side, that is con- 

 tinued as a more or less deep slit through the outer shell ; surface smooth 

 or longitudinally striated. 



This group is difficult to distinguish from Dentalium among fossil spe- 

 cies ; the specimens of which are most generally found with the slender end 

 bearing the characteristic dorsal slit, broken away. Indeed, some concholo- 

 gists deny that this character can be relied upon as a generic distinction in 

 all cases, though there are some slight differences in the animals of these 

 two groups ; while the shell of Entalis is also more generally smooth than 

 that of Dentalium. 



H. and A. Adams retain the name Antalis for this group, citing Aldro- 

 vandus as the author ; while Stoliczka (Palseont. Indica II, 438) retains 

 Aldrovandus's name (writing it Antale), for another type, with a smooth shell, 

 without any posterior dorsal slit, or even eniargination, such as Dentalium 

 tarentinum, Lamarck. He also expresses the opinion that Entalium, De- 

 france, is probably a synonym of this latter group, and not of that hereunder 

 consideration, for which he uses the name Entalis. I have not had access to 

 the necessary works to clear up these points ; but, in any event, I am opposed 

 to going back to Aldrovandus, or any other pre-Linnsean author, as already 

 explained. Consequently, if the shells with a smooth surface and no mar- 

 ginal posterior dorsal slit, such as Dr. Stoliczka ranges under the name Antale, 

 Aldrovandus, are generically distinct from Dentalium proper, they may have 

 to stand under Defrance's name Entalium. 



Shells agreeing in smoothness of surface and general appearance with 

 this group occur as far back as the Carboniferous ; but I am not sure that 

 any of these, or the Permian or Triassic species, really belong to it. Some 

 of the Jurassic forms more probably belong here ; while the genus is repre- 

 sented in the Cretaceous and Tertiary rocks, as well as in our existing 

 seas. 



Dr. Stoliczka has proposed, in the Indian Palseontological Report, II, 

 page 439, for a group including Cretaceous, Tertiary, and recent species of 

 Dcntaliidoe, the name Fustiaria. These are smooth, generally slender shells, 

 only differing from Entalis, as here understood, in having the posterior dorsal 

 slit very deep and sharply linear. I suspect, however, thai this type may nol 

 lie more than subgenerically distinct from Entalis, unless some difference of 

 more importance can be shown to exist in the structure of the animal. 



