134 



more slender form, as well as by its less distinct lines of growth." 

 Both shells, however, were described from imperfect specimens, and 

 under the circumstances, these differences, which after all are only- 

 differences of degree, are pei-haps not much to be relied upon for the 

 discrimination of closely allied species. Meek's latest description of D. 

 gracile would apply almost equally well to D. A^anaimoense, and the same 

 may be said of the brief diagnosis of D. stramineum in the first volume 

 of the Pala}ontology of California, though it is only fair to both writers 

 to add that they may have had reasons for regarding their species as 

 distinct from the present, which ^re not fully stated in their definitions 

 of the former. It is by no means improbable, too, that J), gracile, D. 

 JVanaimoense and JD. stramineum are only geographical and varietal forms 

 of the D. decussatum of Sowerby. 



Entalis Cooperi, Gabb. (Sp.) 



Plate 16, figures 10 and 10a. 

 Dentalium Cooperi, Qabb. — Pal. Cal., Vol. I., p. 139, pi. 29, fig. 100. 



Shell, when full grown, very large, slightly curved ; section circular 

 or nearly so; test extrenaely thick in the middle and at the smaller end. 

 Surface marked by a faint and very minute reticulation, barelj' visible to 

 the naked eye, and produced by minute, parallel, transverse grooves or 

 annulations, which are crossed at right angles by still finer and fainter, 

 longitudinal, impressed lines. In very young specimens the test is quite 

 thin and the reticulation of the surface is barely perceptible, even when 

 examined with a lens. 



North-west side of Hornby Island, in Division D; two miles and 

 a quarter up the Nanaimo Eiver and lowei" part of the Trent River, Y. I., 

 in Division A ; J. Richardson, 1872 and 18Y3. The specimens from the 

 Trent River show that the species must have been very large when 

 perfect, for one shell from this locality, the original of figure 10 on plate 

 16, measures more than three inches and three-quarters in length, and 

 wants nearly three-quarters of an inch of the smaller end. Nearly all 

 the large specimens are much distorted by pressure, but in a single 

 fragment of the posterior half of the shell, an inch and three-quartei s 

 long, which seems to have preserved its normal shape, the small end is 

 fully two lines in diameter and the large nearly four. At the posterior 

 end, therefore, the diameter of the shell appears to become doubled in a 

 length of two inches, but the rate of increase towards the anterior end 

 of adult shells seems to have been less rapid. 



