52 MISSISSIPPIAN BRACHIOPODA 



Remarks. The shells here included in Phillip's species L. analoga have 

 almost always been referred to the supposed long-lived species L. rhom- 

 boidalis. As set forth in the foregoing discussion of the genus Leptcena, 

 it seems best to spilt up this so-called species into several groups of indi- 

 viduals which can conveniently be considered as distinct species. In our 

 Mississippian faunas two such forms are recognized, of which the one here 

 described is the more common. It is referred to Phillip's species because 

 of its apparent identity with that species as illustrated by Davidson, 1 the 

 original definition and figure of Phillips being too imperfect to allow of 

 certain identification. The different individuals of the species exhibit 

 some variation in the coarseness of the concentric corrugations of the 

 shell and in the relative width of the anterior subtruncate margin and 

 the consequent amount of divergence of the lateral margins of the shell, 

 the finer corrugations and the more divergent lateral margins usually 

 being associated. 



Horizon. Kinderhook and Lower Burlington. 



LEPT^NA CONVEXA n. sp. 

 Plate II, Figs. 11-16 



1901. Leptcena rhomb oidalis Weller, Trans. St. Louis Acad. Sci., vol. 11, 

 pp. 159 and 180, pi. 14, figs. 19-20, and pi. 16, figs. 7-8. 



Description. Shell of medium size or somewhat larger, subsemicircular 

 in outline, wider than long, the greatest width at or near the hinge-line, 

 the cardinal extremities usually nearly rectangular. The dimensions of a 

 nearly complete pedicle valve are : length 21 mm., greatest width 28 mm., 

 convexity 8 mm. 



Pedicle valve depressed convex in the umbonal region, this convexity 

 continuing for two-thirds or more of the length of the shell, beyond 

 which it curves more abruptly to the anterior and lateral margins, the 

 surface somewhat compressed towards the cardinal extremities, mesial 

 sinus wanting ; beak small, scarcely produced beyond the cardinal margin 

 and not incurved, perforated at its apex by a small, circular foramen 

 which sometimes becomes filled in mature shells; cardinal area narrow. 

 Internal characters of the vah r e not observed. 



Brachial valve gently concave posteriorly, becoming more strongly 

 curved towards the lateral and anterior margins with no suggestion of 

 a mesial fold or sinus, somewhat flattened towards the cardinal extrem- 

 ities. Internal characters of the valve not observed. 



The surface markings of both valves consist of concentric corrugations 

 which cover the more gently curved posterior portion, these corrugations 

 being either quite regular in their development or exhibiting a con- 



iMon. Brit. Garb. Brach., p. 119, pi. 28, figs. 1-13 (1860). 



