THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 33 



single plate which follows it in turn supports the two large pinnu- 

 lars. This character of two so-called second interbrachials is thor- 

 oughly constant for the species, and is one by which it is readily 

 identified from a fragment, the very few exceptions being clearly 

 sporadic. I have 32 specimens with the plates of the dorsal side 

 preserved, and in only three of them is there a reduction (in some 

 interrays, never in all) of these plates to the single one of other 

 species, one of them being the specimen used by Wachsmuth and 

 vSpringer in describing their species, D. excavatus, wiiich must now 

 go into synonymy. The abnormal specimen from which the de- 

 scription was made was also exceptional in having keellike ridges 

 somewhat similar to those of D. spinosus, from a specimen of which 

 the basal cavity was drawn, that of the type being filled with 

 matrix; so the figure as to this part is incorrect. Both specimens 

 were poor, neither of them typical of the species to which it belonged. 

 Miller and Gurley anticipated the publication with their two fine 

 species, which happily obviates any confusion now, although some 

 authors persisted in using the name D. excavatus, notwithstanding I 

 had privately informed them that the species could not stand. 



The shallow, broader concavity outside of the basal pit usually 

 involves part of the axillary primibrach. The radial series from the 

 edge of the pit slope gradually from their margin to the middle, 

 forming a broad, rounded, sometimes angular, median ridge; and ex- 

 ceptionally in well preserved specimens the two primibrachs are 

 raised into a broad conical node radiately grooved, or rarely into a 

 keellike ridge as in D. spinosus. The surface is more or less sharply 

 sculptured with numerous somewhat sinuous lines and wrinkles. 

 There is considerable variation in this ornament, but it is wholly 

 subordinate to the dominant characters of the species. 



The tegmen is broadly convex, with a slight overhang at the 

 margin, composed of more or less rugose plates, mostly large; but 

 the interambulacral areas are occupied by transverse belts of nar- 

 row, elongate, triangular plates, between the lower, thin apexes of 

 which the numerous pinnule openings emerge. Such long tegmen 

 plates are a feature of all those species having several openings to 

 the interray, and those with the larger number have a slightly over- 

 hanging roof. The relation of the pores, as already discussed, to the 

 fixed pinnules which lead to them is well shown in the lateral views 

 given on plate 7, figures 2, 4, 5. 



D. grandis is a good illustration of the small importance to be 

 attached to minor variations occurring in a form having a few strong 

 and dominant specific characters; modifications of surface struc- 

 ture, for example, which might be utilized toward the differentiation 

 of forms less definitely fixed, may here be wholly disregarded. 



