176 PALAEONTOLOGY OF CALIFOENIA. 



under the beaks ; anterior end narrowly rounded ; posterior end 

 broadly convex; base slightly sloping, and nearly straight; sur- 

 face faintly marked by lines of growth. 



Length, 1.25 inch; width under the beaks, .3 inch; width near the posterior 

 end, .4 inch. 



A rare shell from the Martinez Group, Martinez. 



It can be distinguished from the young of Solen parallelus, by its widening pos- 

 teriorly, and by the prominent beaks. From S. [Hypogella) Diegoensis, it differs 

 in all the details of form. 



S. (H.) Diegoensis, Gabb. 



(S. (Solena) Diegoensis, Gabb; Pal. Cal., Vol. 1, p. 213, pi. 32, fig. 280.) 

 [Plectosolen Diegoensis, Con. ; Smithsonian Check List, No. 240.) 



"When I used Browne's name for this subgenus, I did it without knowing the 

 date of its publication, having been misled by H. and A. Adams. Scientific re- 

 search in a new country, away from large libraries, is attended with great diffi- 

 culties, such as only those who have had the experience, can understand. As 

 I have already intimated elsewhere, I strongly disapprove of the use of pre- 

 Linnasan names in science, believing that the only way to arrive at a settled nom- 

 enclature, is to fix some definite date, behind which we cannot go, as has been 

 done by the British Association. Gray's name of Hypogella is the oldest that we 

 can use according to this rule. The name Plectosolen, was proposed by Mr. Conrad, 

 without a description; and he has since informed me that he has abandoned it, 

 finding it to be founded on untenable characters 



CORBULA, Brug. 

 C. Hornii, Gabb. 



PI. 29, Fig. 62, a, b. 



(C. Hornii, Gabb ; Pal. Cal., Vol. 1, p. 149, pi. 29, fig. 128. 



This species was described from a cast of a left valve and a broken right value, 

 Subsequently Dr. Horn sent me four other specimens, which enable me to correct 

 some points in the diagnosis. The shell is almost exactly equivalve, the anterior 

 end not usually so produced as in the figure quoted above ; the left valve is strongly 

 angulated posteriorly, the right valve not so much so ; the surface is marked by 

 fine and pretty regular concentric lines. 



