26 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



Springer in describing this species makes the following interesting comparison with recent 

 species : 



The stem has a considerable resemblance to that of I. decorus, except in the disposition of the cirri. It must have 

 been quite long, as the longest portion, preserved to a distance of 140 millimeters, shows little sign of any rounding. It 

 is rather more pentagonal for equivalent distances. The cirri are very long and slender; the taper near the base from 

 short and wide joints to long, narrow, and equal ones is quite marked. The most perfect one has 44 joints, and this 

 was probably near the maximum. The interesting thing about the cirri, however, is the fact that they are directed 

 upward instead of downward or outward. In consequence the sockets do not extend to the infranodal (hypozygal) 

 joint, but slope upward toward the supranodal, the lower margin of which is often incised by them. This is more or 

 less the case in the genus Metacrinus, but is not usual in the recent species of Isocrinus, most of which have the cirri 

 directed downward, though in some, as I. listeria and I. wyville-thomsoni, the socket is confined to the nodal joint, and 

 the cirri are given off about horizontally. 



The basals, as shown by the five specimens figured and three others, are quite uniform in their form and propor- 

 tions. They form with the radials a low funnel, with smooth or slightly rounded sides, and without protuberance or 

 projection of any kind. They are connected exteriorly by their lateral faces, giving a pentagonal outline and forming 

 a closed ring [PI. II, fig. 3a], as in the type for which Forbes proposed the genus Cainocrinus, instead of appearing as 

 mere triangular points separated from each other by the radials and tending more or less to project downward over the 

 proximal column joints, as in more recent species. 



The bifurcation of the arms so far beyond the axillary IBr is an unusual feature, occurring in the largest specimen 

 at the twenty-seventh to the thirtieth brachial [PI. II, fig. 1], and in other specimens from the sixteenth to the twenty- 

 third. I know of no pentacrinoid in which arm division takes place so high up; nor in fact any inadunate crinoid, the 

 nearest approach to it being found in the Carboniferous genus Poteriocrinus. There is little tendency of the arms to 

 spread out, but they are long and slender, tending rather to lie in a bundle. The general aspect of calyx and arms is 

 somewhat like that of I. naresianus, which it also resembles in the number and regularity of the syzygies, which is 

 unusual in the Pentacrinidas. I can trace them in two arms of specimen A [PI. II, fig. 1] part way, and in one to the 

 end, and can distinguish them in the distal portion of some other arms. Beginning at IIBr 3 + 4, they occur at inter- 

 vals of mostly about 10 brachials, but sometimes 4, 5, or 6. I give a figure of the pair next to the last, being about 

 brachials 79 + 80 of that arm [PI. II, fig. la]. 



Belated forms. — Springer states that the stem joints of I. Tcnighti — 



are uniformly different from the much larger .ones on which P. asteriscus was founded, and from the Utah specimen 

 referred by Dr. White to P. asteriscus ' but afterwards separated from it by Dr. W. B. Clark under the name Penta- 

 crinus whitei, because of its alternating joints. Clark's camparison was made chiefly with the Red Buttes specimen of 

 P. asteriscus (?), but the separation is doubtless well founded, nevertheless, as the character on which he bases it is 

 clear in his specimen, and cannot be shown in the type of P. asteriscus. The difference between the stem of our species 

 and that of P. whitei is similar to that between the recent J. decorus and I. parrse, which is fairly constant. 



The most nearly related European species that I know of is de Loriol's " Pentacrinus" beaugrandi from the Upper 

 Jurassic, Portlandian stage, near Boulogne-sur-Mer, France. 2 This was the only Crinoid known to the author from 

 the Portlandian stage, and it is the species which he originally proposed to separate from the other Pentacrinidee on 

 account of having a closed ring of basals, under the name Picteticrinus. In this he found himself anticipated by the 

 Cainocrinus of Forbes, and in the work last cited, page 281, he abandoned the distinction, and referred the species to 

 Pentacrinus (sensu P. H. C. ). It has similar large basals, but the arms branch lower down, the stem is more sharply 

 stellate in corresponding portions, and the cirri much more delicate. The stem is preserved to the fourth internode, 

 which has 8 internodals, whereas ours has 14 at the same stage. 



Pentacrinus (Cainocrinus) andrex Desor 3 is similar to the French species, but with shorter basals and shorter 

 internodes. 



Localities. — Medicine Bow (type) and Eed Buttes, Wyo. 



Geologic horizon. — Sundance formation (Shirley stage of Knight), Upper Jurassic. 



Collection. — U. S. National Museum (682). 



Genus PENTACRINUS Blumenbach. 

 Pentacrinus asteriscus Meek and Hayden. 

 Plate III, figure 2. 

 Pentacrinus asteriscus Meek and Hayden, 1858, Acad. Nat. Sci. Philadelphia Proc, vol. 10, p. 49. 

 Pentacrinus asteriscus Meek and Hayden, 1860, Acad. Nat. Sci. Philadelphia Proc, vol. 12, p. 419. 

 Pentacrinus asteriscus Meek, 1864, Smithsonian Misc. Coll., vol. 7 (177), p. 27. 



Pentacrinites asteriscus Meek and Hayden, 1865, Paleontology Upper Missouri, Smithsonian Contr., vol. 14 (172), p. 67, 

 PI. Ill, figs. 2a, 2b. 



1 U. S. Geol. Survey Bull. 97, p. 27, 1893. 



2 Mem. etage Jur. Boulogne-sur-Mer, p. 298, PI. XXVI, figs. 23-25, 1875; Paleontologie francaise, Crinoides, vol. 11, pt. 2, p. 278, PI. CLXXXI, 

 figs. 1-3. 



a De Loriol, Crin. toss, de li Suisse, p. 112. 



