MAZATLAN BIVALVES 



stices being pitted, the whole shell is decussated by very fine 

 rather distant concentric ridges, passing over and between the 

 ribs. The large ventral ribs are hollowed in the interior of 

 the shell. Long. '03, lat. '04, alt. '02. 



Hab. Mazatlan ; one valve in Spondylus washings ; L'pool 

 Col. 



GENUS ? TRAPEZIUM, Megerle. 



Megerle von Muhlfeld, Untwurf&c. p. 68, 1811 -.Phil. Hand. 



Condi, p. 350. 

 Libitina, ScJmm. 1817. 

 Cypricardia, Lam. An. s. Vert. 1819. 



120. ? TRAPEZIUM , sp. ind. 



Tablet 424 contains a puzzling little shell, too young to 

 identify even generically. It is shaped like the adult, not the 

 young of Cardita, but entirely without radiating ribs. Shell 

 transparent, subrhombic, irregular, anteriorly truncate, umbos 

 projecting, lateral ; valves smooth, with a few regular distant 

 concentric epidermal ridges ; inside with a very stout projecting 

 cardinal tooth, fitting between two small ones in the opposite 

 valve, and a posterior lateral tooth in each. Ligament external : 

 no trace of pallial sinus. Long. '02, lat. '04, alt. '03. 

 Hab. Mazatlan ; 1 pair, in shell washings ; L'pool Col* 



FAMILY CHAMHLE. 



This aberrant family is placed by Lam. and Woodw. between 

 Unio and Tridacna ; by D'Orb. between Spondylus and Ostrea ; 

 by Gray between Saxieava and Cardita - T by PhiL between 

 Cardium and Lucina. In its adherent mode of life and irregular 

 growth it resembles Ostrea ; while its two large adductors and 

 its siphons remove it far away. Both animal and shell have 

 relations with Isocardia (Glossidse, Grray) which was, not so 

 unnaturally as might appear at first sight, associated with it 

 by Linnseus. 



* Of the two species of GouHia in the Cumingian Collection, G. cerina, 

 C* S. Ad. is congeneric with the so called ' Circe ' minima, not with the G. Pacifica 

 of the same author. Congeneric with the latter species and with G. varians are 

 Crassatella Martinicensis, D'Orb., intermediate in form between the two Mazat- 

 lan species, and Crassatella Guadaloupensis, D'Orb. the exact analogue of G. 

 Pacifica. For which group the generic name is to be retained, those who hav& 

 seen the diagnosis must decide. 



