420 ME, F. A. EATHEE ON PETAL0CEINT7S. [Aug. 1 898, 



sutures between the branclies. These dots are not shown in PI. XXV, 

 fig, 31, which aims at representing form alone. 



The Stem is known only in P. mirahilis. A single columnal 

 attached to the cup is seen in specimens a, d, and f 2, but is quite 

 obscure in the two latter. In a (PL XXVI, fig. 42) it appears to 

 be subangular, but the direction of the angles is not easy to deter- 

 mine owing to the irregularity of the silicified surface ; it is quite a 

 low ossicle, with a width of about 1 mm, ; its lumen is very small, 

 and appears obscurely pentagonal with radial angles. In specimen c 

 the dorsal cup is covered by very hard matrix, consisting of 

 silicified crinoid fragments. Above the abactinal centre is seen the 

 articular surface of a columnal, similar to those of a, d, and f 2, and 

 certainly belonging to this crown. Apparently it is subpentagonal 

 with interradial angles, but the edges are rounded and irregular, so 

 that one cannot feel certain as to this point. The diameter of this 

 columnal is 1 mm, ; the diameter of its lumen '25 mm. At 4*5 mm. 

 from here, lying interradially, between the arms numbered i and ii, 

 are five columnals, still united one to another, and connected with 

 the central one by fragments of others (PI, XXVI, fig. 50), The 

 length of the fragment of five is 5'2 mm. : that is, the height of a 

 columnal is 1'04 mm. ; its width is 1 mm. Another columnar frag- 

 ment of five ossicles lies in a radial direction at the distal margin 

 of the arm numbered ii ; its measurements are similar to those of 

 the other fragment. A few other columnals of similar appearance, 

 but much worn, are scattered in the neighbourhood. Although 

 there are remains of at least one other crinoid genus close by, these 

 columnals are shown by their size and position to belong to the 

 individual of Petalocrinus. In this case the stem cannot possibly 

 have been less than 22 mm. long ; but it was probably longer, since 

 the width of the crown is 33 mm. The columnals in the first 

 fragment of five show a marked depression at half the height, as 

 though each columnal had been formed by the fusion of two. The 

 sutures are slightly and irregularly crenulate. The articular 

 surface of one of the scattered columnals (PI. XXVI, fig. 49) shows 

 radiating striae ; others are smoother, with slight depressions 

 (PI. XXVI, fig. 48), sometimes giving a subpentagonal outline to 

 the articular surface, which normally is circular. 



The orientation of the angles of the stem and of its lumen in all 

 these specimens can hardly be determined with sufficient certainty 

 to base on it any argument as to the presence or absence of infra- 

 basals ; but there certainly is nothing in the appearance that conflicts 

 with the idea that the crinoid had a dicyclic or pseudo-monocyclic 

 base, with the downward prolongations of the chambered organ 

 radial in position. 



V, Systematic DEscEiPTioisr oe Genus and Species. 



"While it is possible to include in our generic diagnosis the 

 characters of the calyx, which was probably the same in all species, 

 the deficiency of material prevents us from basing the diagnoses of 

 the species on more than the arm-fans. This, it is probable, conceals 



