ACANTHOCHITES. 25 



Var. DiEGOENSis Pilsbry, n. var. Pi. 12, figs. 52, 58, 54. 



Shell oblong, rather elevated, carinated, the side-slopes straight. 

 Color buff or light gray, mottled on the sides with olive or olive- 

 black ; girdle light green with whiter sntural tufts. 



The intermediate valves are rather minutely and acutely beaked 

 when not eroded ; are wide posteriorly, tapering anteriorly, but the 

 girdle does not encroach much at the sutures. Dorsal areas nar- 

 rowly triangular, having about a dozen flattened longitudinal strise 

 separated by narrower grooves. Latero-pleural areas covered with 

 a rather coarse but regular scale-like granulation, the granules flat, 

 oblong. Posterior valve having the tegmentum covering the greater 

 part of the articulamentum, somewhat diamond shaped, tvider than 

 long, with the jjroinine^it mucro at the posterior' third. 



Interior blue-green ; sinus rather wide, angular; sntural laminse 

 moderate sized, rounded. Posterior valve obscurely bilobed behind, 

 gently curved upward in the middle of the posterior insertion plate. 



Girdle (Jig. 53) densely clothed ivith rather long, light green spicules, 

 and having 18 or 20 tufts of longer whiter spicules, the tufts usually 

 not very conspicuous, and sometimes a few of them are lacking. 



Length 19, breadth 9 mill.; divergence 110°. 



Length I82, breadth 8 mill. ; divergence 110°. 



Length 11, breadth 6 mill. ; divergence 110°. 



Sa7i Diego, California (Hemphill.) 



This may })rove to be the adult form of Carpenter's A. avicula ; 

 but on account of the obvious discrepancy between my specimens 

 and his description, it seems best to retain it under a separate name 

 pending the re-examination of Carpenter's type. 



The covering of the whole girdle is more developed than in most 

 species, resembling velvet with a deep pile ; and the tufts are less 

 conspicuous than usual. The pustules are all drop-shaped and flat- 

 topped. Black ones are scattered among the others, which are light 

 colored, often almost whitish. The ridge has ten or a dozen excep- 

 tionally deep longitudinal stride (fig. 54.) 

 A. ARRAGONiTES Carpenter. 



Shell elongated, elevated (at an angle of 110°), pale brown, 

 variedly painted with rose and olivaceous. 



Intermediate valves strongly beaked, the interstices strongly 

 diverging from the beaks ; dorsal area wide, pale, very delicately 

 longitudinally granulate-striate, transversely most minutely corru- 

 gated; lateral areas indistinct; surface all strongly granulated. 



