166 MYAD^E. 



characteristic form and appearance as in the so-called Lutraria 

 oblong a and L. elliptica. 



M. ARENARIA, Linn, et Auctoram. 

 M. arenaria, Brit. Moll. i. p. 168, pi. 10. f. 4, 5, 6. 

 We have not observed this species, "but the recorded ac- 

 counts of it show that it differs little from the type. 



Having ventured to consider Panopcea a superfluous genus, 

 it is impossible that we can for a moment conscientiously 

 maintain a still more unnecessary one, the ft Lutraria " of 

 authors ; our description will show that the present animal is 

 in all essential points a My a ; the differences of the specialties 

 of the soft parts are scarcely worth notice, the cirrhi being 

 red-brown instead of white, and the terminations of the 

 siphons slightly forked, whilst in the type, the M. truncata, 

 there is no separation. The greatest variation between the 

 two is in the hard parts, but I trust, at the present epoch, we 

 are not to adopt precepts of zoology which would be incom- 

 patible with the present position of the sciences ; that because 

 an animal shuts the door of its house by a different-shaped 

 hinge from that of its congener in all other respects, it is to be 

 considered, on that account, generically distinct : we may as 

 well say of two similar doors, that because one has the patent 

 hinges and the other the common sort, they are distinct kinds of 

 objects ; it is the same with the M. oblong a : gentlemen may call 

 its animal by the name of Lutraria, but that does not make it 

 less a Mya. We maintain the position that there is not a 

 trace of generic distinction between the typical Mya and the 

 so-called L. oblonga and L. elliptica, and that there are no 

 more decided specialties between them, than between the 

 species of every other genus. Lutraria has not a malacolo- 

 gical support ; it entirely rests on the artificial grounds of 

 variation of the dentition of the hinge ; for the ligament or 

 cartilage is what is called internal, both in Mya and Lutraria ; 

 we therefore consider that an essential service is done in pro- 

 posing to relieve science of a useless genus, which has not 



