REPORT ON UPPER PALEOZOIC FOSSILS FROM CHINA. 327 



POST-PENNSYLVANIAN (?) SPECIES. 



Dielasma ? cf. D. elongatum Schlotheim. 

 Plate 29, Figures 22-24. 



This form occurs in great abundance at one of the stations where collections 

 were made, and a large number of specimens have passed under examination. It 

 has been found, however, very difficult to secure suitable examples for study, as 

 the rock breaks across the shells as often as around them. In no instance have the 

 two valves been observed in conjunction. 



Probably no example of this form attained a length of 15 mm., and the average 

 appears to be shorter 10 mm. The shape is elongate ovate, the greatest width 

 being some distance back from the anterior margin and the ventral beak being long 

 and pointed. The length is considerably greater than the width. The convexity 

 is moderate to rather strong. While there may be a slight sinuation of the anterior 

 margin when the shell is viewed endwise, no well-marked fold and sinus is manifest 

 in the general curvature. 



That the terebratuloids from this locality show considerable variation, especially 

 in point of relative breadth and convexity, my examination appears to demonstrate, 

 but not how wide is the variation nor how closely connected are the extremes ; for to 

 have uncovered sufficient specimens to reach a well-established conclusion upon 

 these points would have entailed much labor, with relatively uncertain and insig- 

 nificant result. 



The general form of these shells would seem to place them in the group of 

 Dielasma elongatum, though they are almost certainly distinct from that species, 

 differing in having the front more produced and strongly rounded. While quite 

 distinct from typical D. hastatuni, they nevertheless resemble certain figures of that 

 species given by Davidson, especially some which represent small or young examples. 

 The same is true of their relation to typical D. elongatum, from which they differ as 

 above noted ; yet with varieties which have sometimes been referred to Schlotheim's 

 species, they in some instances show many features in common. This is true of 

 some of Davidson's figures. Waagen illustrates 1 a specimen which is similar to the 

 prevailing Chinese form, but is probably broader and with a less slender elongate 

 beak. Tschernyschew figures' 2 two somewhat different types under this title, that 

 represented by his figure 6 of plate n possessing a greater convexity and a less 

 distinctly ovate shape. On plate xi, figures 5, 6, and 7, he shows a form different 

 apparently from the foregoing, different also from at least many Chinese specimens, 

 in being less elongate and more truncated in front. A similar but larger type is 

 shown by his figure 9 of plate iv. 



The Chinese form resembles more closely perhaps the type which he figures as 

 Dielasma bovideus, although it is smaller and does not possess so marked a flattening 

 of the anterior portion of the ventral valve. In this figure, however, Tschernyschew 

 certainly does not represent a veritable example of D. bovidens, still less in figure 4 

 of plate iv. The Chinese form never, so far as observed, is as narrow as that which 

 Tschernyschew represents as D. millepunctatum, being in fact in shape intermediate 

 between that species and D. bovidens and in size much smaller than either. 



It may be remarked that it has been the practice of American paleontologists 

 to place D. millepunctatum in the synonymy of D. bovidens, but this is probably a 

 mistake, and Tschernyschew' s identification, at least in the case of Hall's species, is 

 far closer to the truth than our own usage. 



'Mem. India Geol. Surv., Paleontologia Indica, Salt Range Fossils, vol. i, 1887, plate 25, fig. 10. 

 "Mem. Comite Geol. [Russia], vol. 16, No. 2, 1902. 



