204 CATALOGUE OF THE BLASTOIDEA. 



figs. 13-16), represent a form which is so very different from Troostocrinus or Meta- 

 blastus that we had no hesitation in accepting Triccelocrinus as a valid genus. 



The characters of the type, as given hy Messrs. Meek and Worthen 1 , are so gene- 

 rally applicable to the whole group of species that we here reproduce them. The 

 strongly pentagonal form of the calyx, as seen both from above and from below, is due 

 to the projecting and carinated character of the radial plates. The base is trilobate 

 in general outline, and excavated along the three sutures, the excavations being conti- 

 nued out beyond the base into the lower ends of three of the radial plates (PL XIX. 

 fig. 14). Two of the basals are pentagonal and tricarinate, and one quadrangular 

 and bicarinate, the carinse projecting below the deeply sunken facet for the columnar 

 attachment, so that when placed in its natural position the calyx stands on the carinse 

 like a tripod on its legs (PL XIX. fig. 13). The radial plates are very long and 

 narrow, gradually taper upwards, are very prominent about the middle, and carinate 

 below the lips. The deltoid plates are very small, and the summit openings closely 

 approximate. 



As we can now no longer regard Stephanocrinus as a member of the Blastoidea, 

 Triccelocrinus must be considered as the generic type, in which the peculiarities of the 

 Blastoid base are most strikingly manifested. The distribution of its ridges has 

 been already described on pp. 16-18; and the same arrangement may be traced on 

 the base of many species of Pentremites, Pentremitidea, Mcsoblastus, and Codaster 

 trilobatus (PI. IV. fig. 16 ; PI. V. figs. 8, 11, 14, 29 ; PL VI. figs. 9, 14). In the 

 last-named type (PL XIII. figs. 2, 13) there is an indication of the excavations along 

 the interbasal sutures which reach their maximum in Triccelocrinus. On the other 

 hand, the lower end of the basal cup is cylindrical and not trihedral as in this type ; 

 though this latter character manifests itself very strongly in the allied genus Meta- 

 blastus, especially in forms like M. Varsouviensis and M. Wachsmuthi. Neither of 

 them, however, has the short and more or less truncate base with the deep hollows along 

 the interbasal sutures which are so characteristic of TriccelocrinusWoodmani, the type 

 species of the genus (PI. XIX. figs. 13, 14). These are less marked, though still 

 distinct in our Triccelocrinus Meekianus (PL XVI. figs. 17, 18), and also in T. obli- 

 quatus, Worthen and Meek, which is figured on pi. 31 of the sixth volume of the 

 Illinois Geological Report. Fig. 4 b is a radial view showing the convergence of the 

 two ridges 5 and 6 on to radial D, while 4 d shows the anal intenadius. The figures 

 8 and 9 on the same plate, which represent Pentremites Varsouviensis, show no trace 

 either of these ridges or of any intervening hollows in the base ; and we are a little 

 surprised therefore that the subgeneric name Triccelocrinus should have been 

 appended to the description of the species, which is said by the authors on p. 521 to 

 hi'" closely allied *' to Pentremites, i. e. Mcfahlastus, lineatus. 



1 Report Geol. Survey Illinois, l s 7^'>. vol. v. p. 506. 



