OBOIJD^. 565 



margin, on a line with the anterior portion of the central ridge, there is a narrow elongate 

 space which, under a strong reflected light, is seen to be divided diagonally by a sUght, narrow, 

 raised hne. Compared with Oholus this space is the point of attachment of the transmedian 

 and anterior lateral muscle scars. It is probable that the outside and middle lateral muscle 

 scars and the centrals were attached to the platform, but there are no defined muscle scars 

 upon it. 



The interior of the dorsal valve has several very unusual characters. 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. Waagen [1885, 

 p. 763] calls attention to the resemblance between this process and the tooth of Trimerella 

 lindstromi. From beneath the median process a short, thick platform projects upward and 

 forward into the valve (PI. LXXXI, figs. 2f, 2g, and 2h); it is as wide 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, roimded median septum extends from beneath the platform well toward 

 the front of the shell. Two more or less interrupted and obscure ridges, indicating the main 

 vascular trunks, extend from the front anterolateral angles at the base of and at the side of 

 the platform obhquely outward into the valve. The elongate smooth spaces outlined by 

 Waagen [1885, PI. LXXXY, fig. 6] in Ins illustrations of tliis 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 Oholus. 



Figure 47A, page 567, shows the area, median ridge, and side ridges of the visceral area of the 

 dorsal valve. The platform shown by Plate LXXXI, figure 2f, has not been developed beyond 

 the first stages of its growth. It is probable that the fully developed platform occurs only in 

 very old shells. There is no trace of a platform in the specimen represented by Plate I, figure 

 3, but it may have been broken away. In another shell, not illustrated, there is no trace of 

 thickening beneath the visceral area. , In a section of the platform, median ridge, and vas- 

 cular sinuses taken where they unite with the inner surface of the dorsal valve (fig. 47B, p. 567) 

 the platform appears to be internaediate in development between the platforms represented by 

 figure 47A, page 567, and Plate LXXXI, figure 2f. 



Type. — Neoholus warthi Waagen. 



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

 Survey of India, I received the type specimens of Neoholus, Davidsonella, and LakTiinina, 

 studied, described, and illustrated by 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 can not clearly recognize some of the characters noted by Waagen. 



Waagen's original description [1885, p. 762] of the genus ''Davidsonella" is very full and 

 he also gives a detailed description of the type species "D. linguloides." Oehlert [1887, p. 

 1265] evidently based his description of "Lakhmina" on Waagen's description and illustra- 

 tions, apparently not noting that Waagen stated in his text [1885, p. 762] that the elongate 

 area on the sides of the interior of the shell were not muscle scars, but that he considered them 

 as smooth areas outside the crescent. 



Oehlert [1887, p. 1265], when describing the genus LaTcTimina, says, "with a straight and 

 projecting beak perforated for the passage of the foramen." He reproduces Waagen's figures 

 and shows a deep pedicle furrow. This leads me to think that he had Waagen's description 

 and figures in mind when writing his diagnosis of Lakhmina. Only one shell shows the apex 

 of the ventral valve and the small false area beneath, and one other of the interior shows the 

 true area and a triangular depressed spot at the center; a fracture at the center has broken 



