

242 Messrs. R. Etheridge, Jun., and P. II. Carpenter on 



7. On the Genus Tricoelocrinus, Meek and Worthen. 



Obs. The name Triccehcrinus was suggested by Messrs. 

 Meek and "Worthen* as that of a proposed subgenus of 

 Troostocrinus y Shuin. We have already mentioned that we 

 believe Shumard's genus to be a good one, and have pointed 

 out some other characters which we regard as distinctive of 

 the type f. Messrs. Meek and Worthen, accepting the genus 

 provisionally, described a new species under the name of 

 Pentremites (Troostocrinus?) Woodmani \\ but they pointed 

 out at the same time that it presents some rather strongly 

 marked differences from the typical Troostocrinus ; for " the 

 body is broadest below, while the base is comparatively very 

 short and wide, and has the three spaces corresponding to the 

 flattened sides of the typical species of Troostocrinus so very 

 profoundly and broadly excavated as to impart a very remark- 

 able appearance to the lower part of the fossil." The figures 

 of P. Woodmani represent a type which is so very different 

 from Troostocrinus as understood by Shumard and by our- 

 selves that we have no hesitation in accepting Triccehcrinus 

 as a valid genus. We are somewhat surprised, however, to 

 And P. varsouviensis referred to this type by Meek and 

 Worthen § ; for it is described as being closely allied to P. 

 UneatuSj which is an undoubted Troostocrinus , and the figures 

 given of it show no trace of an excavated base. 



On the other hand, the form figured by Meek and Worthen 

 as Trie, obliquatus \] is a true Triccehcrinus, though we have 

 considerable doubt as to its identity with the species which 

 was described under that name by Romer^f from some iso- 

 lated radial plates. There are some similar plates in the 

 national collection, which we have examined j while we have 

 also obtained a section of a T. Woodmani in Mr. Wachs- 

 muth's collection. These have shown us that throughout 

 the greater part, if not the whole length, of the ambulacra the 

 hydrospiral tubes do not project downwards into the visceral 

 cavity. The radials are very thick and incompletely exca- 

 vated by their median sinuses ; so that the enlarged lower 

 ends of the hydrospiral tubes actually rest on a floor which is 

 formed by the body of the radial, an internal view of one of 

 these plates not having the forked appearance of its outer 

 surface. 



* Illinois Report, vol. v. p. £08. f Loc. cit. pp. 247-249. 



J Loc. c#. pp. 508, 509, pi. xvi. fig. 4. 



§ Illinois Keptrt, vol. vi. p. 521, pi. xxxi. figs. 8 and 9. 



|| Ibid. pi. xxxi. fig. 4. 



f Loc. cit. p. 47 rSGT), Taf. iii. fig. 11. 



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