NATURAL SCIENCES OF PHILADELPHIA. 159 



1. — Strotocrinus, M. and W. (proper.) 



Section (a). Species without a proboscis. — S. periimbrosus* S. recalls and -S^. 

 gli/plus, all described under Actinocrinus by Prof. Hall. 



Section (b). Species with a proboscis. — S . agilops, S. rudis, S. liratus, S. 

 w7ibrosus,f S. tenuiradiatus, S. tholus and S. insculpms, all described by Prof. 

 Hall under Actinocrinus. It may also probably include his Act. glans. His A. 

 clavis is believed to be synonymous with his iS. xgilops (sp.), and his Act. 

 subumbrosus a variety of his S. liratus (sp.) 



2. Subgenus Phtsktocrinps, M. and W. 



r. ventricosus, P. cancellatus^ P. ornatus and P. reticulatus, all described by 

 Prof. Hall nnder Actinocrinus ; a.\so P. subventricosus, described by Professor 

 McChesney under Actinocrinus. The proposed species senarius, Hall, is be- 

 lieved to be a variety of his A. ornatus. 



In the single character of having only a simple opening in the vault, with- 

 out the slightest indications of a proboscis, the Physeiocrinus group would 

 agree more nearly with the typical section (a) of Strotocrinus than the section 

 (b) does, but in all other characters it is more distinct. 



Section (C). 

 Strotocrinus ectypcs, M. and W. 



Body depressed, very rapidly expanding to the third radials, above which 

 the seconaary and tertiary radials and brachial pieces curve out horizon- 

 tally. Base about twice and a half as wide as high, truncated, slightly con- 

 cave, and not expanded or thickened below, but with small nodes around the 

 margin of the under side, placed one at the termination of each of the costte. 

 First radial pieces wider than high, two heptagonal and three hexagonal. 

 Second radials one-half to two-thirds as large as the first, wider than high, 

 hexagonal, or in part (sometimes) pentagonal, the superior lateral sides 

 being short. Third radials wider than long, pentagonal, hexagonal, or irreg- 

 ularly heptagonal, and supporting on each superior sloping side a secondary 

 radial, each of which gives origin to brachial pieces leading to an arm on 

 the outer side, and supports on its inner sloping side a tertiary radial, which 

 gives origin to two arms, thus making three arms to each main division, or 

 six to each ray, and thirty to the entire series. 



First anal piece a little longer than wide, hexagonal, and supporting two 

 pieces of about half its own size in the next range : between the superior 

 sloping inner sides of these there is one small piece, and above these three 

 or four other small pieces, one or two of which extend up so as to separate 

 slightly the outer brachial pieces of the adjacent rays. Interradial pieces 

 four or five to each area, the upper of which is narrow and extends up so as 

 to separate slightly the brachial pieces above. In each interaxillary space 

 there is usually an elongated intercalated piece, sometimes large enough to 

 truncate slightly the upper margin of the third primary radial, while it con- 

 tinues upward so as to separate the brachial pieces above. 



Vault much depressed, and composed of numerous, irregular, slightly con- 

 vex pieces of moderate size, and provided with a rather stout subcentral pro- 

 boscis, composed near the base of unequal pieces, some of which are distinct- 

 ly protuberant. 



Surface of all the body plates moderately convex, or sometimes a little 

 angular in the centre, and ornamented with distinct radiating costte, extend- 

 ing from the middle to the sides of each piece, so as to divide the whole into 

 numerous triangles. These costae are also more or less compound, so as to 

 form a secondary or (below the middle of the first radials) a tertiary series of 

 smaller, less defined triangles within those formed by the principal costae. 



*See vol. ii, Geological Report Illinois, p. 188, 1866. 

 t Iowa Report, part 11, pi. ii, fig. 3, a b. 



18690 



