74 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



The interior of the dorsal valve has several very unusual char- 

 acters. There is no true cardinal area, unless the thick margin of 

 the shell be considered as such. From the center of the cardinal 

 margin a strong flat process, marked by concentric lines of growth, 

 projects forward into the valve and rises a little above the plane of 

 the margin of the valve. Dr. Waagen [1885, p. 763] calls attention 

 to the resemblance between this process and the tooth of TrimcreUa 

 Vindstrdmi. From beneath the median process a short thick plat- 

 form projects upward and forward into the valve; it is as w'ide as 

 the process at its base, expanding toward its front margin. It is 

 concave between its lateral crests, and the outer slopes are slightly 

 ■concave from the crest to the body of the shell. In front the 

 ■concave space and crests terminate rather abruptly above the front 

 face, which in turn is underlain by a transversely hollow space of 

 unknown extension beneath the platform. Toward each end of the 

 frontal area a minute depression appears to indicate the point of 

 attachment of a muscle. A narrow, rounded median septum extends 

 from beneath the platform w^ell toward the front of the shell. Two 

 more or less interrupted and obscure ridges, indicating the main 

 vascular trunks, extend from the front antero-lateral angles at the 

 base of and at the side of the platform obliquely outward into the 

 valve. The elongate smooth spaces outlined by Dr. Waagen [1885, 

 pi. Lxxxv^ fig. 6] in his illustrations of this valve are too indefinite 

 to be given form in the drawing of the only specimen showing the 

 interior. What appears to be a small muscle scar occurs at the 

 cardinal angle ; it corresponds in position to the transmedian scar of 

 Ohohis. 



Type. — Ncoholus warthi Waagen. 



Observations. — Through the courtesy of Dr. T. H. Holland, 

 Director of the Geological Survey of India, I received the type speci- 

 mens of Ncoholus, Daz'idsoiicUa, and Lakhmina, studied, described, 

 and illustrated by Dr. Waagen. With these before me, I find that 

 the elaborate figures of Waagen [1885, pi. lxxxv] are diagrammatic 

 to a considerable extent ; also that I cannot clearly recognize some of 

 the characters noted by Dr. Waagen. 



Dr. Waagen's original description [1885, p. 762] of the genus 

 "Davidsonclla" is very full and he also gives a detailed description of 

 the type species "D. Unguloides." Dr. Oihlert [1887, p. 1265] evi- 

 dently based his description of "Lakhmina' on Waagen's description 

 and illustrations, apparently not noting that Waagen stated in his 

 text [1885, p. 762] that the elongate areas on the sides of the inte- 

 rior of the shell were not muscle scars, but that he considered them 



