The Rogers Gap Fauna of Central Kentucky 131 



which Strophomena planoconvexa, although described earUer, is 

 only a weaker, less vigorous form. 



15 — Hchertella latasulcata, sp. nov. (Plate III, Figs. 7A, B; 

 exterior and interior of pedicel valve.) — Shell attaining a length 

 of 26 mm. and a width of 35 mm., though usually only about 30 

 mm. in width. The median part of the brachial valve often is 

 elevated along the anterior half of the shell into a fairly prom- 

 inent fold. The valve, in general, is quite strongly convex, and 

 the beak is quite strongly incurved. The most striking external 

 feature is shown by the pedicel valve. This is comparatively flat, 

 does not have a high cardinal area, and, hence, does not have a 

 prominent beak. The latter is moderately incurved. The median 

 sinus or depression is remarkably wade and shallow except close 

 to the anterior margin, where it adjoins the fold of the brachial 

 valve. The radiating plications are rather numerous, with only 

 a moderate tendency toward grouping into fascicles on the pedicel 

 valve, and even less on the brachial valve. Cardinal and crural 

 plates of the brachial valve sharp and thin ; muscular markings 

 very faint or obsolete. The muscular area of the pedicel valve 

 tends to be narrower, especially anteriorly, and hence has a less 

 cordate outline than the more typical forms of Hehertella occid ent- 

 ails and H. sinnata. The muscular area, moreover, is less deeply 

 impressed, especially anteriorly. Specimens of this type occur in 

 the cut south of Rogers Gap and at 59.3, 58.5, 58.3 ; are typically 

 developed at 58.1 ; and occur also at 57.8, 57.6, 57.4, 56.8, 56.4, 55.7, 

 55.0, and 54.2. It is not a strongly defined species, but belongs to 

 the series recently called, by some paleontologists, mutations. The 

 absence of Hehertella in the Eden at Cincinnati should here be 

 noted. 



16 — Platystrophia cf. colbiensis, Foerste — A small form of 

 Plat\strophia, resembling Platystrophia colbiensis, occurs at 59.1, 

 54.5, and 54.3 miles from Ludlow. It usually does not exceed 

 15 mm. in length, and is associated with occasional specimens, 

 having a very short hingeline, which eventually may turn out to 

 be an Orthorhynchula, but sufficiently good specimens to admit of 

 accurate determination have not been found as yet. Illustrations 



27 



