238 PROCEEDINGS OF THE ACADEMY OF [1888. 



factorily made out, but it is certain, however, that in some groups at 

 least, it does not possess specifically such an important classificatory 

 value as has been generally supposed. 



Pleurotomaria modesta nov. sp. (Plate XII, figs. 2a, 2b.) 



Shell small, sublenticular, spire greatly depressed, volutions six, 

 obliquely flattened above; body whorl very large, rapidly increasing 

 in size, sharply angular on the periphery, flattened or very slightly 

 concave above, prominently rounded below, suture line linear ; 

 spiral band very narrow almost linear, very slightly impressed and 

 occupying a position just above the peripheral angle ; on the spire 

 the band is obscured by a single series of conspicuous nodes ; aper- 

 ture subquadrate, or subrhombic ; umbilical region slightly im- 

 pressed, but not perforated ; surfjice glabrate ; under a glass exhib- 

 iting fine lines of groAvth ; the last whorl with a series of small 

 transverse folds, or wrinkles, toward the tuberculated margin ; each 

 fold apparently originating at a node and extending about one-half 

 or two-thirds the distance to the periphery. 



Twenty or more specimens of this beautiful little species have 

 been obtained from the black superimposing shales of coal No. 3. 

 It approaches more closely than to any other the form described by 

 Cox as P. depressa and may eventually prove identical with that 

 form. P. depressa, however, was preoccupied by Phillips in 1836; 

 and this name was also used by de Koninck and by Passy. 



Pleurotomaria grayvillensis Norwood and Pratten. 



Pleurotomaria grayvillensis Norwood and Pratten, 1855. Jour. 

 Acad. Nat. Sci. Phila., vol. Ill, p. 75. 



Pleurotomaria grayvillensis Geinitz, 1866. Carb. und Dyas in 

 Nebraska, p. 9. 



Shell rather small, conical subovate, longer than wide ; spire 

 moderately elevated ; whorls five to seven, obliquely flattened above. 

 Body whorl large, rapidly increasing in size, rounded below ; bian- 

 gular around the periphery, both angles being visible on the spire. 

 Aperture subrhombic ; outer margin sharp. Columella extended 

 below. Surface ornamented by from twenty-five to forty revolving 

 lines, of which twenty or more occupy the inferior surface of the 

 body whorl ; some of the lines are much more prominent than 

 others, and there is a more or less regular alternation of the more 

 prominent ones with less prominent raised stride; these are 

 crossed by numerous somewhat regular lines of growth, giving a 

 more or less tuberculate appearance, which is most conspicuous 



