36 PROCEEDINGS OF THE ACADEMY OF [1887. 



portion of the hinge of both valves of the adult examples of the 

 type species is marked by crenulations or denticles, which cross 

 the hinge at nearly right angles in front but at the posterior por- 

 tion their course is obliquely downward and backward. 



In the type species a small blunt tooth is observable at the 

 anterior end of the hinge of the left valve ; and there is a larger, 

 more oblique one at the posterior end of the hinge. There are 

 corresponding pits in the left valve to receive these teeth, and 

 some specimens also show a slight elevation at the side of the 

 anterior and posterior dental j^its respectively, suggesting that 

 they represent incipient teeth in that valve. Byssal aperture 

 obscure or absent. 



This genus agrees with Perna in .the characters which have 

 already been mentioned, but it differs from Perna in the retreat- 

 ing position of the beak, in the projecting instead of inflected 

 anterior extremity of the shell beneath the beaks, in the crenula- 

 lation of the articulating portion of the hinge, in the smaller 

 number of ligamental pits, and in the absence of a well-defined 

 byssal notch in either valve. 



It agrees with Margaritophora, as shown, for example, by the 

 living species M. pica Gould, from the southern Pacific Ocean, in 

 the character of the test, in the muscular markings, in the pos- 

 session of blunt teeth upon the anterior and posterior portions of 

 the hinge, and in the retreating position of the beaks. It differs 

 from Margaritophora in having well-developed ligamental pits in 

 its hinge areas, a crenulate or denticulate, instead of a smooth 

 hinge border, and in the absence of a compressed anterior ear, 

 and of a distinct byssal notch. 



Bakevellia has some characteristics similar to those of this 

 genus, but its ligamental pits are fewer in number and occupy 

 only the middle portion of the hinge, while its lateral teeth are 

 two or three in number at each end of the hinge, and they are 

 nearly parallel to the hinge border ; the latter being smooth and 

 not crenulate. Besides this there is some reason to doubt whether 

 Bakevellia really belongs to the family Aviculidse, as do Perna 

 and its congeners ; and to which family this new genus is 

 referred. 



The si)ecies which is described in the following paragraph is 

 proposed as the type of Aguileria. Senor Aguilera has shown 

 me some examples of a species which he obtained from the Cre- 



