24 ACANTHOCHITES. 



plate. Posterior valve having the tegmentum very small, ovate, 

 narrower in front, longer than ivicle, mucro situated at the posterior 

 third. 



Interior blue, darker along the cavity ; sinus narrow, deep, sub- 

 angular. Sutural laminae very large. Posterior valve biangular 

 behind, strongly contracted on the latero-posterior sides. 



Girdle very wide, covering all but a narrow shield of each valve ; 

 covered with a close, short velvety pile which has a lon'ger fringe 

 around each valve ; bearing 18 unusually large, dense tujts of exces- 

 sively fine spicules, usually 5-7 7nill. long. 



Length 25-30, breadth 15-18 mill. 



La Paz, Lower California (W. N. Lockington.) 



This is one of the largest as well as the most beautiful species of 

 the genus. The valves are more covered than in any other known 

 form, and the bunches of shining bristles are larger. A large 

 number of individuals preserved in alcohol and dry were presented to 

 the Academy by Mr. \y. N. Lockington, (no. 60107.) 



One specimen before me has the girdle pubescence of a pale buff 

 tint, and the tufts are silvery, a trifle bronzed. 



Var. AMPULLACEUS Pilsbry. PI. 4, fig. 85. 



Similar to the preceding, but exposed portion (tegmentum) of 

 intermediate valves much broader behind, flask-shaped ; the lateral 

 borders sigmoid. Tegmentum of anterior valve also larger. 



A. AVicuEA Carpenter. 



Shell very similar to A. arragonites in form, size, girdle and 

 general habit; but the sculpture and terminal laminae are different. 

 Dorsal ridge having about 6 longitudinal grooves, the intervals 

 appearing flatly scaled ; umbones wide ; diagonal areas hardly 

 defined ; sides ornamented with oval, flattened scales, large for the 

 size of the shell, and in indistinct diverging series. Mucro small, 

 situated in front. Color livid and olivaceous-brown variously 

 stained. Plates of insertion at sides as in A. arragonites ; anterior 

 plate with 5 slits. 



Length 4, breadth 2 J mill. {Cpr.) 



Catalina Lsland, 10-20 fms. ; rare (Cal. State Coll., no. 1072. 

 Cooper.) 



AcantJwchites avicula Cpr., Proc. Cal. Acad. Nat. Sci. iii, p. 211 

 (Feb., 1866.) 



Like A. arragonites, but valves sculptured in large snake-skin 

 pattern, ( Cp)r.') 



