NATURAL SCIENCES OF PHILADELPHIA. 153 



each one of which is succeeded by another. Upon the superior sloping sides 

 of the latter, in the anterior and one of the lateral rays, commence the brachial 

 pieces, of which there are two ranges, upon the last of which commence the 

 free arms, thus giving origin to four arms in each of these rays. In the two 

 posterior rays, however, and one of the lateral, after the second bifurcation 

 on the last secondary radial, the latter supports on the outer sloping side a 

 tertiary radial, which gives origin to two brachial pieces, making live arms to 

 each of these rays, or twenty-three to the whole series. 



After the first bifurcation on the third radial pieces, all the succeeding 

 pieces of each ray are in di ect contact, so as to leave no spaces for interaxil- 

 lary plates : while the outer brachial pieces of each two contiguous rays con- 

 nect over the anal aud interradial spaces, so as to nearly or quite isolate the 

 pieces filling those spaces, from the dome. 



First anal piece of the same form as the subradials, but rather smaller than 

 those of the anterior and antero-lateral rays ; surmounted by three smaller 

 hexagonal and heptagonal pieces in the second range, and three or four in the 

 third, making seven or eight altogether. Interradial pieces four, (rarely five, ) 

 those of the inferior range being larger than the others. 



Surface without costse or visible granules, but roughened by the tubercular 

 character of the plates. The tubercle occupying each first radial and the first 

 anal, is larger than those on any of the other pieces of the side walls above ; 

 where they become smaller and less distinct with each succeeding range, un- 

 til they are nearly or quite obsolete a few ranges below the arms. Upon the 

 dome, however, the tubercles are prominent and well defined. The proboscis 

 is unknown, but its base is stout, and rises rather abruptly from the dome, 

 being placed nearly its own breadth nearer the anal than the opposite side. 



The arms are also unknown. They evidently projected at first horizontally 

 outwards from the body, and their bases are so crowded as to form an almost 

 continuous rim around the body. 



Height from base to horizon of arm openings, about Ot)4 inch ; height to 

 base of proboscis, 1*22 inches. Breadth of dilated margin of base, 0-46 inch ; 

 breadth of same just above, 0-38 ; breadth of body at top of first radials, 0-55 

 inch ; breadth of same at arm openings, 1"05 inches ; breadth of base of pro- 

 boscis, 0'43 inch. 



This species belongs to a peculiar group of Actinocritius, as generally under- 

 stood in this country, of which A. piriformis, tthumard, (Missouri 

 Report, pi. A, figs. 6a, b, ) may be regarded as the type. It also includes 

 our A. pistilliformis* and A. clavigerus, Hall. These species differ remark- 

 ably in form from typical species of Actinocrinus, such as A. triacontadactylus, 

 A. lavis, &c, of the old world, in having the body very narrow and attenuate 

 below the arms, so as to form, as it were, a kind of handle to the upper half, 

 giving the whole, when the arms and pioboscis are removed, somewhat the 

 form and appearance of a pestle. They also differ from the old world species 

 regarded as typical forms of Actinocrinus, in having the arms springing from 

 the body in a continuous series, instead of being in five groups. Should it be 

 considered desirable to separate this little group as a section of Actinocrinus, it 

 may be called Uperocrinus, from its resemblance, when the arms and proboscis 

 are removed, to a short-handled pestle. If Casseday's group Batocrinus, bow- 

 ever, should be adopted as a distinct genus from Actinocrinus, this should be 

 ranged under it as a subgenus. 



Specifically, the form under consideration differs from A. piriformis in 

 having its first anal, first radial, and basal pieces, proportionally much 

 shorter, its base more flattened below, and more dilated around the margin ; 



* In indicating this form under the name A. rudis, (Proc. Acad. Nat. Sci , Juue, 1S61, p. 131,) 

 we ha'l over ooked the fact of that name having been used by Prof. Hall for another species, in 

 the tfupplemuuc of the; Iowa Report, p. 33: hence we now propose to call it A. pialiUi/urrais. 



18U5.] 



