the Morpliology of the Blastoidea. 247 



Granaiocrinus granulosus ^ Meek & Worthen. Keokuk 

 group (Subcarboniferous), Illinois. 



Pentremites missouriensisj iSliumard. Chemung (Devo- 

 nian), Missouri. 



Granatocrinus 2vqjectus, Meek & Worthen. Burlington 

 group (Subcarboniferous), Iowa. 



Pentremites Potte.ri^ Hanibach. Ditto. 



With the exception of one species, S. missouri'ensis, which is 

 found in the Chemung group (a division of the North-Ame- 

 rican Devonian), the whole of the species are of Carboniferous 

 age, and confined to America. 



Genus TeoostocPvINUS, Shumard, 1865. 



Troostocrinvs, Shumard, Traus. St. Louis Acad. 1865, ii. p. 384 (note) ; 

 Meek & Worthen, Illinois Geoi. Keport, 1873, v. p. 507. 



Ohs. This genus was proposed bj Dr. Shumard, in his 

 useful Catalogue of North-American Palseozoic fossils, for 

 subfusiform species o1 Pentremites^ after the type of P. Rein- 

 wardtiij Say, possessing a slender outline, triangular base, 

 and linear ambulacra. The genus was never described in 

 detail, but was adopted by Messrs. Meek ahd Worthen pro- 

 visionally. To it they ascribe species with a triangular base, 

 flattened on all three sides, a narrow fusiform body, elongate 

 and tapering below, and narrow ambulacra. 



Dr. Shumard's remarks arc as follows : — " There appear 

 to me good reasons for removing this and other subfusiform 

 species, as Pentremites Peinxcanltii^ P. lineatus^ P. hijpyra- 

 midalis, P. Wortheni, and perhaps P. Grosvenorij from among 

 the Pentremites, and grouping them together in a separate 

 subsection under another name. These and allied forms are 

 remarkable for their slender subfusiform shape, linear pseud- 

 ambulacral fields, triangular base, and simple summit-struc- 

 ture. These external differences would seem to imply cor- 

 responding modifications in the internal economy of the animals 

 of more than specific importance. If, from a more thorough 

 study of such species, it should be deemed advisable to separate 

 them from the genus Pentremites, I would propose the name 

 Troostocrinus for the group," &c.* 



In this proposal we entirely concur ; but as our acquain- 

 tance with the genus depends simply on the structure of T. 

 Pieimoardtii and T. lineatus, we shall confine our descriptive 

 remarks to these species. The most important morphological 

 difference between Troostocrinus and Pentremites lies iu the 



* Loc. cit. 



18* 



