730 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvii. 



Aside from the typical species, whose characters have been detailed 

 above, there can probably be referred to PleurophweUa several forms 

 resting- at present with different generic groups. One, a species pos- 

 sessing many of the essential characters of rienrophoreUa^ was described 

 as Alletnsmaf gilher'ti White. This author neglects to mention the 

 presence in this species of a depressed lunule and of a strongly marked 

 ligamcntal area. The surface, furthermore, is marked by granules 

 arranged in radial lines and having the appearance of delicate lirje. 

 While the lunule in this species is depressed, it is not nearly so deeply 

 concave as in PleurojyJiorclJai^apillosa. Another species, less perfectly 

 known than AUerisma gilberti but without nmch doubt belonging to 

 the same generic group, is AUerisma geinitzi Meek. On account of 

 the preservation of the tj'pe of this species man}'^ of the parts shown in 

 Allerisina gilherti are concealed. AUerisiiia refiexum, which appears 

 from Meek's figures to be very closely related to Allerisma gilherti^ 

 probably does not belong here, the type specimen being ver}^ imperfect 

 and Meek's figure possibly misleading. Allerisma costatum of Meek 

 and Worthen, which is so similar to PleurojyJioreUa fapUlosa that one 

 species might possibl}^ be mistaken for the other, belongs, it is very 

 probable, to the same group, and Allerisma lanceolatum Swallow also 

 is a possible representative of Pleurophorella^ although the description, 

 which is unaccompanied by figures, permits no more than a surmise 

 upon this point. 



The incongruit}^ of some of the forms referred b}" American authors 

 to Allerisma has been remarked even by Europeans, and I find that 

 Wheelton Hind has rejected several American species originally 

 referred to King-'s genus. Among these is Allerisma hannilxtlensis 

 Shumard, long since transferred to Grammysia. By an oversight it 

 would seem he accepts the original description of Allerisma costatum 

 Meek and Worthen as a true member of the genus, and rejects the 

 rei)ublication in 1873 and also a later identification from Ohio. As 

 the later descriptions were accompanied by figures, which were lack- 

 ing to the original one, the rejection of this species probabl}^ repre- 

 sents his best founded opinion. He also rejects Allerisma jpleuropistlia 

 Meek, Allerisma winchelli Meek, and Allerisma ventricosmn Meek. 

 Allerisma illinoiseiise Worthen is likewise thrown out, and either 

 Allerisma andrewsi or Allerisrtiamaxvillense — of the two without much 

 dou))t Allerisma andrewsi. 



Hind's rejection of Allerisma costatum is of importance to me be- 

 cause of the similarit}^ of that species to the type of Pleurophorella\ 

 and in connection with the relationship of Pleuropliorella to Aller- 

 isma. He neither excludes nor includes the other species which at 

 present seem to be appropriately assigned with Allerisma costatum to 

 the genus Plenrop>liorellu. Relieved of these forms and those men- 

 tioned by Hind, one of which, however, can possibly be retained in 



