INVERTEBRATES. 363 



PUKTKEMITIDEA*, D'Orbigny. 



1849. D'Orbigny. Prodrome do Palaeont, p. 102. 



1K5X D'Orbigny, Cours Elemontaire, i>. M 1 .'. 



I SSL'. KtlirridKr and Carp., Ann. and Mag, Nat. Hist.. i>. L'.'II. 



PENTREMITIDEA AMERICANA, Barris, Nov. Sp. 



Body small pyriform, height twice the greatest width, which is 

 across the radial lips. Ab-oral side in form of a cone with slightly 

 convex sides, triangular at the end, hut gradually assuming a 

 strongly marked pentalobate aspect, actinal side of the body equal 

 in length to the ab-actinal side ; curving gently in an upward direc- 

 tion; broadly truncate and somewhat depressed at the oro-anal re- 

 gions. 



Basals forming a triangular vace, with rounded angles, and of a 

 height greater than the width at the top, upper edges slightly con- 

 cave. 



Eadials two-thirds the length of the body, a little more sloping 

 than the basals; width at basi-radial suture equal to the width of 

 the plates at the opposite side. The forks occupy two-thirds the 

 length of the plates, are comparatively narrow, and end in a sharp 

 point which constitutes the uppermost part of the entire body. The 

 sides toward the sinus are elevated and formed into sharp edges 

 which stand out at right angles above the ambulacra. Kadial lips 

 prominent. 



The oral plates are not observed in a side view, they are extremely 

 small, and are placed against the tips of two adjoining limbs, within 

 the truncation of the peristome, where they form a narrow rim 

 around the spiracles. 



Ambulacra broadly linear, the lateral sides depressed, and forming 

 a deep sulcus ; the inner portions almost on a level with the forked 

 plates, except near the mouth, where the whole ambulacrum lies 

 deeper than the surrounding plates. 



Spiracles ovate, drawn out in a sharp angle, pointing to and sit- 

 uate close to, the mouth. They are placed within the oral plates, 

 taking up almost their whole surface, leaving exposed a very narrow 



*The genus Peiitn>inili<lea differs from Troostocrinus, Shumard, its nearest allied 

 form, in having quite inconspicuous oral plates, always placed within the truncate upper 

 face of the body, and only five spiracles; which are strictly interradial; while in Trootto- 

 fi-iiius the orals are always visible in a side view of the specimen, and there are ten slit- 

 like spiracles along the lateral edge of the ambulacra, and a separate anal opening. I 

 am indebted to Mr. Wachsmuth for the recognition of the above species as Pentremiti- 

 dea, and who claims that it i.s the first one that has been discovered in America. 



