DESCRIPTION'S OF Till' SI'F.CTE8. 203 



only three arc represented in the diagram given l>y GEhlert ', which is as correcl as 

 we could wisli. But it is scarcely possible to define a new genus of Blastoids by tin- 

 single character of a tripartite base which is common to the whole class ; and though 

 we refer the type to Metablastus for t lie present, it may prove to be a different 

 genus when its summit characters are known. 



Locality and Horizon. Bois-Roux, Commune de Gahard, Ille-et-Vilaine, France: 

 (ires de Gahard, Lower Devonian. (Presented by Dr. P. II. Carpenter, P. U.S.) 



Genus T1UCCELOCRINUS, Meek & Worthen, 1SG8. 



Triccehcrinus, M. & W., Proc. Acad. Nat. Sci. Philad. 18G8, p. 356. 

 Tricadocrinus, M. & W., Report Geol. Survey Illinois, 1873, vol. v. p. 5(36. 

 Trkwloc rin us, E. & C, Ann. & Mag. Nat. Hist. 1883, vol. xi. p. 242. 



Gen. Char. Calyx pyramidal, or pyramidal subovate, broadest below and narrowing 

 upwards; summit always small, and much contracted; base short and moderately 

 wide, trihedral at its lower end, and excavated more or less deeply along the inter- 

 basal sutures, the excavations extending for a greater or less length on to the surfaces 

 of three of the radials. Basal plates carinate and more or less hollowed laterally. 

 Radial plates thick, always long and narrow, and more or less carinate in the middle 

 line below the radial lips, three of them being partially excavated below the carina' ; 

 sinuses narrow and deep, but not penetrating through the thickness of the radials except 

 near the summit. Deltoid plates small and probably confined to the summit within 

 the radial limbs. Ambulacra usually long, remarkably narrow, or linear, and deeply 

 situated in the sinuses; side and outer side plates minute. Hydrospires small, not 

 pendent, but enclosed within the substance of the radial plates for the greater part 

 of their length. Anterior spiracles small, more or less completely divided, and situated 

 close round the mouth ; the two posterior spiracles separate both from one another 

 and from the anus. Mouth small. Anus large. Column circular. 



History. The name Triccelocrinus was suggested by Messrs. Meek and Worthen in 

 1868 as a proposed subgenus of Troostocrinus, Shumard, for a type in which "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 Troosto- 

 crinus so very profoundly and broadly excavated as to impart a very remarkable 

 appearance to the lower part of the fossil." 



In 1883 we adopted Tricadocrinus as a genus, and gave some further details of its 

 structure, more especially with reference to the hydrospires. 



Remarks. The figures of Tricoelocrinus Woodmani' 2 , the type of the genus (PL XIX. 



1 Bull. Soc. Geol. de France, 1882, tome x. p. 362. 



- Report Geol. Survey Illinois, 1873, vol. v. pi. xvi. fig. 4. 



•Jd 2 



