MAZATLAN BIVALVES 



a Gastrochsena truncata in its burrow, and a Petricola robusta 

 which, after penetrating to the Frock, has flattened itself 

 rather than bore into the harder substance. 



122. CHAMA SPINOSA, Brod. 



Proc. ZooL Soc. 1834, p. 150. Eve. Conch. Icon, in loc. 



Three small valves and one pair appear to belong to this 

 species. The valves differ from the young of C. frond, fornicata, 

 in having the entire surface crowded with semi-tubular spines ; 

 and in the character of the margin, which is smooth and 

 rounded within, outside with crowded scales one on another, 

 like the base of Hipponyx tessellata. The types and the pair 

 do not display this structure, which appears very characteristic. 

 Hinge teeth comparatively small ; muscular scars not very 

 large ; colour white, with slight rosy tint at the umbos which 

 are scarcely spiral. Long. 1*1, lat. I'l, alt. '08. 

 Hob. Lord Hood's Island, Cuming- ? Mazatlan ; extremely 



rare ; L'pool Col. 



Tablet 444 contains a valve. The pair will be seen, attached 

 to Ostrea, with Discina, on tablet 20. 



123. CHAMA PEXOGYRA, Conr. 



One broken pair attached to a pebble, and a valve on Spondy- 

 lus calcifer in the Liverpool Museum, differ from the rest of 

 the Mazatlan Chamse in the following particulars. Shell sinis- 

 tral ; ventrally produced ; surface roughened and laminated, 

 not spinous ; margin smooth, rounded off, slightly crenate 

 outside ; teeth long, small, colour reddish brown, without 

 purple. They may belong to Ch. Panamensis, or even to Ch. 

 corrugata,'but seem best to accord with this species. Long. 1 * 5, 

 lat. 1'17, alt. 1'15. 



Hab Sta. Barbara, San Diego, &c. Nuttall Mazatlan ; ex- 

 tremely rare ; L'pool Col. 

 Tablet 445 contains the specimen on pebble. 



FAMILY CAEDIAD^E. 



GENUS CAHDIUM, Linn. 



Only two species of this abundant genus were sent in any 

 quantity ; the shell washings however proved that many more 

 must exist in the neighbourhood ; 5 species being found suf- 



