ENTOMOLOGY. 



cular thai? 0. subriifa and more so than O. mo7ioetis ; unlike either 

 it is produced a little obliquely to one side, while having two ears of 

 nearly equal magnitude, it is at once distinguished from Monoetis 

 which has invariably no more than one ear, or at least the other is so 

 small as to justify the appellation of Monoetis. This presence of two 

 distinct ears therefore again removes it nearer to O. subrufa ; but in 

 admitting the Ostrea subrufa to be the nearest of those two analogies to 

 the present shell, it will be found to possess another character which 

 separates it still more remotely than monoetis, namely, the number of 

 longitudinal rays, for in the present shell there are no less than 

 thirty of those rays, while in O. subrufa there are no more than 

 twenty. In this latter particular our shell accords with O. Monoetis, 

 for the usual number of rays in that shell is thirty, and by 

 this means that species is once again brought into the alliance. But 

 having so far pointed out the distinctions that apply only alternately 

 to one of those species or to the other, we arrive at one which dis- 

 tinctly removes our present shell from either, namely, the charac- 

 teristic features of those longitudinal ribs in the three species 

 respectively : in Ostrea subrufa they are only slightly elevated, 

 broad and glabrous ; in monoetis raised narrow and somewhat angular, 

 the centre of the rib being fiat, and the ribs as well as the grooves 

 between them being transversely intersected with large raised 

 arched spines, which are placed at a moderate distance from each 

 other, and are sufficiently conspicuous in the perfect or unworn 

 shell ; in our present shell, the spines should rather be denominated 

 prickles, they are extremely small, inconspicuous, and closely set, 

 and are consequently extremely numerous in comparison with those 

 of Ostrea monoetis. We should further add, that in our present 

 shell the longitudinal rays are not flat, but form an acute ridge down 



