CARBONIFEROUS AGE. PERMIAN PERIOD. 61 



The only specimens of this species we have seen, are internal casts, which give 

 no idea of the surface markings. We have also been unable to make out the nature 

 of the muscular and pallial impressions, and have therefore only placed it in this 

 genus from the close analogy of its form to typical species in more recent formations. 



Locality and position. — Near the mouth of Smoky Hill fork of Kansas River, 

 and on Cotton-Wood Creek, as well as at other localities in the Permian beds of 

 northeastern Kansas. (Type 3957.) 



Family CRASSATELLIDJE. (See page 34.) 



Genus PLEUROPHORUS, King, 1844. (See page 34.) 



PEenrophorus f subcuneatus. 



.^Plate II, Fig. 3.) 



Plemophorus subcuneatus, Meek & Hatden, Trans. Albany Inst. IV, Maroh 2d, 1858. 

 Pleurophorus ? subcuneatus, Meek & Hayden, Proceed. Acad. Nat. Soi. Phila. June, 1859, 29. 



Shell small, longitudinally oblong, the basal and cardinal margins being parallel, and the extremities rather nar- 

 rowly rounded ; valves moderately convex ; beaks depressed, and located near the anterior end. Hinge long, 

 straight, or slightly arched ; cardinal teeth unknown ; posterior lateral teeth parallel to the hinge margin, and 

 remote from the cardinal teeth. Impression of the anterior adductor muscle deep, subtrigonal, and located close 

 to the margin — internal ridge on its posterior side well defined, ranging nearly vertically ; impression of the pedal 

 muscle distinct from, and located directly over, that of the anterior adductor; posterior muscular impression very 

 faint. Surface with fine concentric striae. 



Length of a medium sized specimen, 0.54 inch ; height, 0.24 inch ; thickness or convexity, 0.16 inch. 



In form and general appearance, as well as in the character and position of its 

 anterior adductor muscuk^r scars, and its posterior lateral teeth, internal ridge, &c., 

 this species agrees quite weU with the typical species of Prof King's group Pleuro- 

 phorus. It differs, however, in having the scar of its anterior pedal muscle nearly 

 marginal, instead of farcher back, while the casts show scarcely any traces of the 

 radiating costse generally well marked on those of that genus. 



It also agrees very closely with a small shell figured by J. de C. Sowerby, 

 under the name of Unio j)haseolus (Trans. Geol. Soc. Lond. 2d ser. vol. V, p. 491), 

 and subsequently referred, by Prof. Koninck, to the genus Cardinia. Indeed these 

 shells are so closely similar, that, judging from the figures and descriptions we have 

 seen of the European form, we have some doubts whether they may not prove to 

 be specifically identical. We think it scarcely possible that they can belong to 

 different genera. Possibly both should be referred to Carhonocola, McCoy ( = 

 Anthracosia, King). 



This species wiU be kno"vvn from our P. occide?iialis, by its greater height in the 

 anterior region, and more prominent antero-ventral border. It also seems to differ 

 in being, as above stated, nearly or quite destitute of the radiating plications seen 

 on that shell. 



Locality and positicm. — Near the mouth of Smoky Hill fork of Kansas River ; 

 at the head of Cotton-Wood Creek, and at numerous other localities in north-eastern 

 Kansas. From layers of yellow Magnesian Limestone of Permian age. (Type 4181.) 



