NO. 1372. NEW CARBONIFEROUS MOLLUSKS—GIRTY. 731 



AUerisma, the American crroup of Allorisinata looain.sj somewhat 

 greater homogeneit3\ Some species can with .safety be retained in 

 the genus, as, for example, AUerisma termlnale^ Allerisma mhcuveatum 

 (= Allerisma terminale)^ Allerisma cajMx, Allerimuielomjatum^ Aller- 

 isma andrewsi^ Allerisma clavatum, Allerisma maxvilhmsc, and Aller- 

 isma siivuatxim. Several forms aside from those withdrawn under 

 Pleuropli<rrella^ can be almost certainly rejected, e. g., Allerisma 

 cooperi^ Allerisma granosurn, Allerisma curtum, AlUrisma latnm, 

 Allerisma pleuropistJia^ Allerisma ventricosum, and Allerisma vyinch<:lH. 

 The position of the remaining forms seems to me more or less doul)t- 

 ful. A few will probably remain with Allerisma^ but the major 

 portion will probably bring up elsewhere. The figures in many 

 instances are suggestive of Bphenotus. 



The t^'pe species of Pleurophorella is so unlike a tj'pical Allerisma 

 such as Allerisma subcuneatum {= Allerisma terminale) that the possi- 

 bility of their belonging to the same genus seems at first very remote. 

 It was in fact some time before I recognized the affinity which almost 

 certainly exists between Pleurophcyrella and Alle?'isma. I am at pres- 

 ent not sure that the former should hold the position of more than a 

 subgenus. Both are transversel}' elongate in form, both have a shell 

 marked with papilhe and by concentric folds, both have lunule and 

 escutcheon fairly strongly marked. The lunule in Pleurophorella 

 jKipillosa is not only sharpl^'^ delined but retreats inward to such an 

 extent that in a full-grown specimen the anterior end is conca\e l)v as 

 much as 6 mm. The luiuile is strongly marked and depressed in Pleu- 

 rophella (/ilherti, but to no such marked degree. It is a distinct fea- 

 ture of Allerisma suhcuneatum^ but is not very sharply defined and is 

 not concave. The surface of Pleurophdhi papillosn is finely papillose, 

 with some tendency toward arrangement in radiating lines. \\\ Aller- 

 isma subcuneatum^ and 1 believe in Allerisma generalh', the granules 

 are coarser, much more scattering, and more linear in arrangement. 

 One character wdiich seems to be constant in PUurophordla but is never 

 found in Allerisma so far as I am aware, is the presence of one or more 

 costa^ on the \ipper posterior portion of the shell, a feature which gives 

 much individualit}' of expression to the former genus. It is to be 

 regretted that the interior structures of Pleurophorella are up to tiie 

 present unknown, but those of an external character are sullicieiitly 

 marked to make me look rather confidently for correspomling ditlVr- 

 ences upon the inside of the shell. The costatc condition and general 

 expression of Pleurophorella are very sugge>^tive of ani)ther altogether 

 different group, and Pleurophorella p<fpillo.^a in particular much resem- 

 bles Pleurophorus tropidophorus^ or even Pleurophorus occidenfalis 

 and Pleuroj>horus aiujuhdus ])ut the reseml)lance is only superficial. 

 P/6^u/'o/>/iry/'«w has neither the papillose surface nor the iinpn>ssed luiude 

 of Pleurophm-ella, while if the latter is, as I feel Utile doubt, related 

 to Allerisma the internal structures are ilisfinctly dillerent. 



