NATURAL SCIENCES OF PHILADELPHIA. li. r > 



are not clearly satisfied that this is the case, we merely call attention to it as 

 a variety of C. Shumardi. 



Locality and position, same as last. 



CRINOIDEA. 



Genus POROCRINUS, Billings, 1856. 



Porocrinus, Billings, Report Geol. Survey of Canada, 1856, p. 279 ; Canadiau 

 Org. Rem. 1859, Decade iw, p. 33. 



Generic formula. Basal plates 5. Proper interradials 0. 



Subradials 5. Anals . 2. 



Radials 1x5. 



"Cup conical; basal plates five, pentagonal; subradials five, three hexa- 

 gonal and two heptagonal ; primary radials five ; one large azygos interradial 

 supported on the truncated summit of the anterior subradial, and one small 

 one, situated over the suture between the anterior subradials, and having 

 above it on one side the large azygos, and on the other the left anterior primary 

 radial; several small pectinate! rhombs similar to those of the C)Jstidea. ,, 

 [Billings]. 



As remarked by Mr. Billings, this genus has the structure, so far as the 

 form and arrangement of the plates forming the base and lateral walls of the 

 cup are concerned, of Poteriocrinus and Cyathocriims ; from botli of which it 

 differs in the important character of having pectinated openings analogous to 

 those of the Cystidea. 



Our specimens of the following described species also show that this inte- 

 resting type also presents another character in common with some of the Cys- 

 tidea that is, the possession of several large rounded, non-pectinated open- 

 ings above. Of these openings there are three, one on the anal side, and two 

 on the anterior side. They are all nearly on the same horizon as the bases of 

 the free arms, though the anal opening is a little lower than the other two. 



So it would seem this genus presents, as it were, a combination of the cha- 

 racters of the Orinoidea and Cystidea. With the regularity of structure and 

 arrangement of parts of a true Crinoid, it has the pectinated and other open- 

 ings of a Cystidean. It differs, however, from the Cystidea in having the pec- 

 tinated openings located at the junction of the corners of the plates, instead 

 of passing through them near one of the sides, while the little bars protecting 

 these openings are arranged obliquely, instead of at right angles to the mar- 

 gins of the plates, as in the Cystidea. 



Our species also shows that the conical form of the cup is not a generic 

 character. 



POROCRINUS CKASSOS, M. & W. 



Body subovoid or a little higher than wide. Base depressed, rather widely 

 truncated below, pentagonal in outline, two and a half to three times as wide 

 as high, with a comparatively large pentagonal central perforation ; basal 

 pieces wider than long, pentagonal in outline. Subradial pieces twice to 

 three times as large as the basal, about as high as wide, three hexagonal, and 

 two on the anal side heptagonal. First radial pieces of about the same size 

 as the subradials, apparently all irregularly heptagonal, each with, near its 

 upper extremity, a small outward sloping subcordate, or oval, flattened sur- 

 face for the articulation of the second (first free) radial piece ; four of them 

 with each* one, and the fifth with two, of the superior lateral margins deeply 

 sinuous and forming in part the margins of the large rounded openings of the 

 summit. Anal pieces two ; the first smaller than the other, quadrangular in 

 form, resting between the superior sloping sides of two of the subradials, 

 and supporting, on its right upper sloping edge, one side of one of the first 

 radials, and on its left one of the oblique sides of the second anal piece. 



1865.] 



