38 Dr. J. E. Gray on some Families of Bivalve Shells. 



Fam. 4. PetricolidjE. 



Shell ovate, white, covered with a thin hard periostraca. The 

 cardinal teeth 3 • 2 (one often obsolete), bent up as if coming 

 from the inner surface of the shell under the umbo, the middle 

 one deeply bifid ; lateral teeth none, or rudimentary, marginal. 

 Siphonal inflection deep, rounded. Mantle lobes united, with a 

 small anterior slit. Siphons two, elongate, united at the base. 

 Aperture ciliated. Foot small, thin, cylindrical, with a distinct 

 byssus. 



1. Petricola, Lamk., Gray, /. c. no. 556. Cardinal teeth rather 

 compressed. P. Lithophaga, Lamk. 



This shell must not be confounded with the boring Tapes = 

 {Rupellaria, Bellev.), which have three regular compressed teeth 

 on each valve. 



2. Naranio. Shell ovate, equivalve, inequilateral, swollen, 

 rugose, tubercular, costated behind ; umbo anterior. Cardinal 

 teeth of right valve two, oblique, the upper compressed, elon- 

 gate ; of left valve triangular, oblique, bifid. Lateral teeth none. 

 Cartilage external, short, in a slightly sunken groove. Siphonal 

 inflection very large, rounded; anterior scar oblong, hinder 

 very large, roundish. 



These shells have nearly the external appearance and hinge of 

 Coralliophaga, but are easily known by the large siphonal in- 

 flection. They are generally covered with a calcareous secretion, 

 which hides the rugosities on the surface, and live in stony corals. 



\. N. costata. Surface covered with zigzag grooves and cos- 

 tated in frent. From the West Indies. 



3. N. radiata. Surface covered with radiating grooves. Japan. 



Fam. 5. Corbiculad^, Gray, P. Z. Soc. 1847, 184. 



Cardinal teeth 3*3 or 2*2, diverging ; lateral teeth com- 

 pressed. Siphonal inflection none. Periostraca olive, hard, 

 brittle, often polished. Siphons contractile. 



A. Cardinal teeth 3 * 3, front of right and hinder of left valve 

 smallest. Shell solid. 



1. Corbicula, Megerle, Gray, P. Z. S. 1847, n. 552. Shell 

 subcordate ; lateral teeth compressed, subequal, finely striated. 

 C. fluminea. 



^ 2. Batissa. Shell subcordate ; lateral teeth compressed, 

 striated, front veiy short, hinder elongate. B. tenebrosa. B. 

 obesa, Hinds. 



3. Velorit^, Gray, Syn. B.M. 1842, 75 ; P. Z. S. 1847,n.554. 

 Shell cordate, triangular, thick ; teeth large, lateral, very finely 



