140 MISSISSIPPIAN BRACHIOPODA 



with the spine bases smaller and less numerous, although this latter 

 character may be more or less dependent upon the state of preservation. 

 Martin's type specimens of punctatus were evidently collected in the 

 "Mountain limestone", a formation equivalent to our Mississippian, 

 and among his original illustrations the larger specimens seem to agree 

 well with the shells from the Keokuk limestone, so that it is possible 

 that his name should be applied to the shells here under consideration and 

 a different name assigned to the Pennsylvanian shells. As to the identity 

 of Norwood and Pratten's P. alternatus with Hall's P. vittatus, there can 

 be no doubt; the identity of Swallow's P. gradatus is less certain, al- 

 though it is probably a synonym also. Some specimens from the St. Louis 

 limestone have a shorter hinge-line and narrower umbo, approaching 

 more nearly the Pennsylvanian shells, and should perhaps be excluded 

 from this species. 



Horizon. Burlington limestone, Keokuk limestone, ?St. Louis limestone, 

 and ?0kaw formation of the Chester group. 



ECHINOCONCHUS GENEVIEVENSIS n. Sp. 



Plate XVIII, Figs. 1-6 



Description. Shell a little above medium size, broader than long, the 

 hinge-line much shorter than the greatest width, the greatest width 

 anterior to the mid-length. The dimensions of a nearly complete pedicle 

 valve are: length from hinge-line to front margin 22.2 mm., length from 

 umbonal region to front margin 27.6 mm., greatest width 31 mm., length 

 of hinge-line 21 mm., convexity 31 mm. 



Pedicle valve strongly convex with the greatest depth posterior to the 

 middle, the umbonal region prominent but rather narrow, protuberant 

 posteriorly beyond the hinge-line, the surface curving abruptly to the 

 cardinal margin, curving more gently to the lateral and anterior margins, 

 only slightly compressed towards the cardinal extremities; mesial sinus 

 originating posteriorly in the umbonal region, it is of only moderate width 

 and depth, rounded in the bottom and ill defined laterally ; the beak 

 rather small, pointed and strongly incurved. Surface marked by regular, 

 more or less well-defined, concentric bands from two to four millimeters 

 in width, upon which are the elongate bases of fine, crowded, appressed 

 spines, those near the front of each band being finer than those situated 

 posteriorly. 



Brachial valve gently concave throughout, except towards the cardinal 

 extremities, which are flattened, near or posterior to the middle of the 

 valve, a low, rounded, mesial fold originates which becomes a little 

 stronger towards the front. The surface marked by concentric bands 

 and appressed spines similar to those of the opposite valve. 



