136 Cincmnati Society of Natural History 



of the shell posteriorly. Anterior to this nmbonal ridge, from the 

 appressed beaks to the basal margin, the shell is strongly flattened, 

 the mesial sinus being almost obsolete. Posteriorly, the shell is 

 not obliquely truncated, but the basal margin rounds strongly into 

 the much less convex and very oblique posterior margin, without 

 any indication of straightening anywhere. The shell apparently 

 gapped anteriorly and posteriorly, but this can not be verified with 

 certainty. . 



27 — At 59.7 and 59.1 miles from Ludlow there are found 

 larger forms of Orthodesma, 12 mm. in thickness from valve to 

 valve, which evidently belong to the same group as Orthodesma 

 rectum. All of the specimens found so far are fragments, but 

 the original length must have been at least 60 mm. There are 

 evidences of concentric markings, but these are more numerous 

 and much less distinct than in the form resembling Orthodesma 

 suhnasutiim, and for the present these larger forms are considered 

 distinct. ^ 



28 — The anterior part of an Orthodesma (Plate III, Fig. 2), 

 belonging to the same division of the genus as Orthodesma nasu- 

 tum, Conrad, was found at the railroad cut 59.1 miles from Lud- 

 low. 



About 20 imiles northeast of Rogers Gap, at the railroad cut 

 one mile north of the station at Cynthiana, a nearly entire valve 

 of a similar species (Plate III, Fig. 1) was found, which, however, 

 may not be identical. Compared with Orthodesma nasutum, Con- 

 rad, the Cynthiana specimen is a little higher ; more convex, es- 

 pecially along the hingeline toward the beak, where the shell is 

 incurved ; posteriorly, the hingeline curves downward into the 

 posterior margin at a greater distance from the beak, thus pro- 

 ducing a more sub-parallel effect between the cardinal and basal 

 margins. 



29 — Lyrodesma subplanum, Ulrich — Several specimens 

 which may be referred to this species were found at the railroad 

 cut 59.1 miles from Ludlow. The species was described from the 

 beds below the Fulton horizon at Covington, opposite Cincinnati. 

 The species is figured on plate 47 of the Geologv of Ohio, volume 

 VII. 



32 



