"162 PROCEEDINGS OF THE ACADEMY OP 



rently belonging to that group, that has its body so narrow and produced 

 below, and its body plates presenting the style of angularly sculpturing. If 

 the interradial and anal sinuses of its disc were filled with intercalated pieces 

 it would present nearly all the characters of a typical Strotocrinus. Conse- 

 quently it may be regarded as a connecting link between these groups, and 

 with a few others shows that they cannot be properly separated more thaa 

 subgenerically. 



Locality and position. Upper beds Burlington group of Lower Carbonifer- 

 ous, at Burlington, Iowa. No. 67 of Mr. Waehsmuth's collection. 



Strotocrinus (Physetocrincs) dilatatus, M. and "W. 



Body rapidly expanding, with nearly straight sides, from the base to the 

 secondaiy radials, thence spreading more abruptly to the brachial pieces, 

 which are directed out nearly horizontally, and so closely crowded all around 

 as to come very nearly, or sometimes quite, in contact over the anal and in- 

 terradial areas. Base about three times as wide as high, not thickened or 

 expanded below, but provided with a large round perforation. First radial 

 pieces comparatively large, generally wider than high, two heptagonal and 

 three liexagonal. Second radials only about half as large as tlie first, some 

 of them quadrangular, and others with one or both of the upper lateral angles 

 a little truncated, so as to make them properly pentagonal or hexagonal. 

 Third radials larger than the second, wider than long, pentagonal, hexagonal 

 or heptagonal, and supporting on each superior sloping side a secondary ra- 

 dial, each of which gives origin on its outer side to brachial pieces leading to 

 an arm, while on its inner side a tertiary radial gives origin to two arms in 

 all but the two posterior rays, where one or sometimes both bear on one side 

 another axillary piece, making seven or eigbt arms in each of these rays, or, 

 in the latter cases, thirty-four arms to the entire series. 



First anal piece as large as the largest first radial pieces, and bearing above 

 iwo heptagonal or octagonal pieces of near its own size in the second range, 

 with three smaller pieces in the third range, and two or three minute pieces 

 over these, one of which is wedged in between the brachial pieces above. 

 Pirst interradial pieces generally larger than the second radials, heptagonal 

 ■ or octagonal, and surmounted by two smaller pieces in the second range, over 

 vwhich we usually see one or two small pieces wedged up between the outer 

 brachial pieces of the rays on each side. There is also usually a small inter- 

 axillary piece between the secondary radials of each ray, but it seems never 

 large enough to extend down so far as to truncate the upper angle of auy of 

 the third primary radials. 



Arms stout, increasing a little upward for a distance of two and a half 

 inches (as far as they can be seen in the specimen), each passing directly into 

 a double series of very short pieces, from their origin on the last brachial 

 piece. 



Surface of body plates merely finely granular where ncjt worn, slightly 

 convex, with shallow indentations at their corners. Vault unknown. 



Height of body to the top of tertiary radials, 0-75 inch ; breadth, about 1'33 

 inch ; breadth of arms two inches above their bases, 0-'20 inch. 



This species is related to S. [Fhysetocr.) subventricosuH, McChesney (sp.), but 

 differs in having its bodj^ much more rapidly expanding, and proportionally 

 •wider above, while its tertiary and brachial pieces curve much more strongly 

 outward. It also differs in the relative size and form of its second radial pieces, 

 which are proportionally smaller, and generally quadrangular, or only with 

 the upper lateral angles slightly truncated, instead of being larger and regu- 

 larly hexagonaL Its arras are likewise stouter than those of McChesney's 

 species, judging from the brachial pieces seen in specimens of the latter, 

 while it has one or two arms more in each of the posterior rays. Its surface 

 markings are also different, but this is a very variable character in this group. 



[July, 



