220 PEOCBEDINGS OF THE MALACOLOGICAL SOCIETY. 



The form to which, rightly or wrongly, I restricted the name 

 pusillum of Jenyns, and which will have to take the new name, is 

 a polymorphic one that seems to have puzzled malacologists, some 

 of whom apparently regard it as an extreme form of nitidum. Truly 

 it has much in common with that species; nevertheless, it appears 

 to me to possess certain constant hinge characters, which justify 

 its separation under a distinctive name. Its characteristics were 

 duly set forth in the " Catalogue ", p. 61, but the more salient 

 features of typical examples may well be repeated here. 



Externally the species is glossy, greyer than nitidum, more nearly 

 equilateral than any of the other species, save personatum, with 

 fairly prominent umbones ; the nepionic shell is tolerably large, 

 smooth, and frequently irridescent, and generally immediately 

 followed by a series of concentric ridges as in nitidium, but much 

 stronger. 



Internally this form differs from all others in its hinge. The lateral 

 teeth strike the eye at once as being somewhat longer, narrower, and 

 less prominent than in most of the other species, while their apices 

 are almost at the end furthest from the umbo. The paired laterals of 

 the right valve are more equal in each pair in length than in other 

 species, and stand out from each other a.nd the shell margin. The 

 cardinal teeth are flat-topped and practically parallel with the hinge 

 line ; the base of c ii is continuous with aii and c iv is mainly parallel 

 with it ; c Hi is only slightly curved. The essential arrangement of 

 the cardinals, therefore, recalls that in suhtruncatum. 



PisiDiUM OBTUSALASTEUM, nom. nov., vice P. ohtusale, C. Pfeiffer 

 (of Jenyns non PfeifEer) non Lamarck. 



Jenyns (Trans. Camb. Phil. Soc, iv, 1832, p. 301, pi. xx, f. 1-3) 

 identified his well-marked species with that described by C. Pfeiffer 

 (Naturg. Deutsch.L.-u. Siissw.-Moll, i, 1821, p. 125, pi. v, f. 21, 22) 

 who took the name from, whilst querying its identity with, the 

 Cyclas ohtusalis of Lamarck (Hist. Anim. s. Vert., v, 1818, p. 599). 



There is no certainty as to the identification of either Lamarck's 

 or Pfeiffer's shell, and neither adequately suggests Jenyns', con- 

 sequently the name of Jenyns' shell has to be changed. 



