DESCRIPTIONS OF THE SPECIES. 151 



Mitra (pare), Cumberland, Reliquiae Conservata:, 182(>, p. 81. 



Pentremitea (pars), McQoy, Synop. Carb. Lamest. Foss. Ireland, 1 8 it, p. i?i. 



Pentremites, Goldfuss, Petrefacta Germanise, L826, Theil i- p. ICO. 



I'< iitntfi matites Floreales (pars), Roemer, Arcbiv I'. Naturgesch. 1851, Jabrg. wii. Bd. i. 



p. 35:5. 

 Pentremites, Lyon, Owen's 3rd Kentucky Geol. Report, L857, p. 468. 

 Pentremitea (pars), Pictet, Traits de Pal. 1S.">7, tome iv. p. 292. 

 Pentremites (pars). Hall, [owa Geol. Survey Report, 1858, vol. i. pt. :.', p. 89. 

 Pentremites, Lyon, Trans. St. Louis Aead. Sei. I860, vol. i. no. I, p. 628. 

 Pentremites (pars), Dujardin & Hupe", Hist. Nat. Zooph. Echinod. 1862, p. 89. 

 Pentremitea (pars), Billings, American Journ. Sci. 1809, vol. xlviii. p. 80, 1<S~<), vol. 1. p. 226. 

 Pentremitea (pars), Miller, Cat. American Pal. Foss. 1877, p. 85. 

 Pentremitea (pars), Zittel, Handb. Pal. 1879, Bd. i. Lief. 3, p. 131, 

 Pentremitea, E. & C, Ann. & Mag. Nat. Hist. 1882, vol. ix. p. 219. 



Gen. Char. Calyx variable in size and form, but usually ovate or pyriform, or 

 some combination of the two ; summit broad, or more or less contracted, sometimes 

 truncated and flat, seldom convex ; base occasionally subtruncate, but more frequently 

 elongate and cuplike, never distinctly trilobate, nor excavated in the middle line ; 

 section always more or less pentagonal, and either with straight sides, or the latter 

 occupied by slight re-entering angles ; periphery variable, sometimes at the radial 

 lips, but more frequently equatorial, or nearly so. Basal plates small, forming a 

 small cup, which varies in outline from shallow basin-shaped to depressed funnel- 

 shaped, but these plates never form more than a third of the calyx, and seldom even 

 so much. Radial plates long, usually forming by far the greater portion of the calyx, 

 and of variable convexity ; bodies usually small, seldom equalling the limbs in length, 

 and often subcarinate in the middle line ; limbs long, with flat or concave sides, and 

 always obliquely truncated above ; sinuses broad and subpetaloid, of variable length, 

 and frequently with sharp erect margins; lips simple, or sometimes thickened and 

 projecting. Deltoid plates always small, irregularly rhombic, or lanceolate, some- 

 times concave in the middle line, never horizontal, or produced above into tube-like 

 extensions. Ambulacra broad, subpetaloid, either flat or convex, and sometimes 

 rather deeply sunken in the sinuses ; lancet-plates elongate, somewhat triangular in 

 section, resting below on under lancet-plates, and usually forming about a third of 

 the entire width of the ambulacra, but not wholly filling the sinuses, and flat or 

 slightly convex on their exposed surfaces. Side plates and outer side plates numerous, 

 of variable form, and more or less developed according to species, the former abutting 

 against the edges of the lancet-plates. The hydrospire-pores partially excavated out 

 of the sides of the sinuses ; pinnules attached between the pores, and formed of a 

 single or partially double row of small plates; hydrospires variable in number, from 

 three to nine, pendent, but partially contained within the substance of the radial plates 

 near their distal ends. Spiracles single, but occasionally double, usually more or less 



