156 SMITHSONIAN INSTITUTION 



Calpiocrinus intermedius n. sp. 

 Plate VII, figs. 1-3 



Small, but larger than the next following species. Crown ovoid, broadly 

 rounded below, widest about upper IIBr, where height to width is about 1 to 2, 

 narrowing rapidly from there to an apex; spread of calyx from base to IAx, 

 1 to 2.8. Base rather narrow; side outline strongly convex. Surface smooth. 

 Maximum crown, 30 mm. high by 20 mm. wide ; base, 6 mm. 



IBB greatly enlarged, usually covering the basals except the apex of 

 post. B. BB small; post. B angular above and not touching anal x. RR large, 

 connecting above post. B. IIBr 3 or 4; IIIBr 4 or 5. Average height to width 

 of Br about 1 to 3. Rami unequal, the inner ones of the ray smallest; rounded, 

 strongly tapering, rather closely abutting, infolding to a small apex above the 

 fourth or fifth ramule. Ramules on outer arm of ray about every fourth or 

 fifth Br; inner arm resembling an enlarged ramule with subordinate ramules 

 not visible from dorsal side. Anal x not touching post. B and not larger than 

 first iBr in regular areas; iBr one rather short, broad plate followed by more 

 than one series of small plates abreast. Column large, short, terminating in an 

 expanded encrusting root ; composed near the calyx of prominent short, rounded 

 columnals, with one to three shorter and narrower ones interposed, all becoming 

 short and about uniform toward the distal end. 



This species, like the next, represents a modification in arm structure from Homalo- 

 crinus toward Calpiocrinus in the enlargement of the lower ramules of the dichotom, and has 

 also an infrabasal development sufficient to cover all the regular basals, and any possible 

 radianal. It is clearly intermediate in position, and upon the visible characters might be 

 placed under Homalocrinus, but for the probable absence of a radianal. In the basal struc- 

 ture it goes a step further than any other species, to a quite unusual condition in which the 

 anal x does not touch the posterior basal, but is cut off both externally and internally by the 

 meeting of the two posterior radials below it. Thus although anal structures are present, the 

 posterior basal is not touched or truncated by them, but remains angular, without any distal 

 connection. 



This feature is constant for the three specimens, and is found elsewhere only in the 

 genus Cleistocrinus from the same horizon. 



In arm structure this form is much in the condition of Homalocrinus liljevalli, but in 

 addition to having longer intervals between the ramules there is a perceptible difference in 

 general appearance — the rays in this having a more decided and graceful taper. This is well 

 shown by the beautiful specimen illustrated on Plate VII, figure la, which is the finest and 

 most complete example of this type yet found. It is wholly free from the matrix and is but 

 little flattened by pressure, so that the natural contour is correctly shown. It has what is so 

 rarely found in this group, a perfect stem, with the root complete — a broad spreading struc- 

 ture evidently for attachment to other objects. The stem is very short, as was probably the 

 case with most of the Silurian genera of this group, indicating that they lived in shallow 

 water. The accompanying specimen, figure 2, with the stem almost complete, is from a very 

 fine, somewhat flattened specimen in the British Museum, the largest one that has been 

 found. The third specimen, from which we obtain a satisfactory elucidation of the basal 



