TRUNCATELLA. 385 



ranged in transverse order. The only difference observable in 

 the two species is, that in this, the leaf appears of a shorter or 

 more oval contour, more compact, and with a less deep con- 

 striction ; the neck and rostrum have no additions beyond the 

 groove and aiinulations. Foot thick, having a more elongated 

 oval shape than in its congener, and, as in it, rounded in front 

 and behind on the march ; it simulates the same transverse 

 crease or line on the sole, and has a like character of pro- 

 gression. There is a simple, almost terminal, but decided 

 operculigerous lobe that bears a light corneous suboval oper- 

 culum, which in all points, except being of lighter colour and 

 broader oval, is identical with that organ in the preceding 

 species, to which I refer ; indeed, so great is the similarity of 

 the two animals, that I might, by a reference, have condensed 

 the greater part of this account; but as these notes are 

 decidedly comparative of tAvo particular creatures, I have 

 given them in extenso. The animal is free, but deliberate 

 on the march, and carries its shell very upright, at nearly an 

 angle of 75-80 from the horizon. 



It will be seen that this account is essentially the same as 

 the one in the 'British Mollusca/ except that the learned 

 authors have proposed to deposit it in Assiminia. I think its 

 generic position is with Truncatella. A comparison of the 

 two species will show that they are not only identical in the 

 principal characters, but that almost all the minutise are con- 

 gruous. Indeed I may say, that these gentlemen differ from 

 me little more than in the name, ' Assiminia,' which I would 

 gladly accept for Truncatella for the reasons below, if such 

 a change in nomenclature were not forbidden by strict con- 

 ventional laws. As far as I can learn, not having seen the 

 animal of A. Gray ana, the genus Assiminia scarcely varies, if 

 at all, from Truncatella ; at least the generic characters given 

 in the ' British Mollusca ' are absolutely those of that genus, 

 except some difference in the position of the eyes, which I 

 should not be surprised to find greater in terms than in reality. 



The generic title of Truncatella is objectionable, as being 

 in this case too distinctive, and therefore only strictly appli- 

 cable to Truncatella Montagui, whilst two, if not three, of our 



2 c 



