80 FOSSIL ECHINI OF THE WEST INDIES. 



Eocene, San Fernando formation, Vitabella Road, Mount Moriah, 

 San Fernando, Trinidad, J. A. Bullbrook collector, 1 specimen, U. S. 

 Geol. Sur. station 8878; U. S. Nat. Mus. No. 328225. 



Genus PERIASTER d'Orbigny, 1854. 



Type species. — Periaster conicus d'Orbigny, 1854, Paleontologie 

 Francaise, vol. 6, p. 274, plate 899. 



The genus Periaster is very dubious. Duncan considers it a synonym 

 of Linthia. Apparently no type-species has ever been definitely desig- 

 nated for the genus. If Periaster conicus d'Orbigny be now designated 

 as the type, then the genus can be recognized and Cotteau's Periaster 

 elongatus from St. Bartholomew can be considered as a valid Periaster. 

 Cotteau says that the genus Periaster is distinguished from Schizaster 

 by the fact that its posterior ambulacra are ordinarily more elongate. 



Periaster elongatus Cotteau. 

 (Plate 13, Figure 11.) 



Periaster elongatus Cotteau, 1875, Kongl. Sven. Vet. Akad. Handl., vol 13, No. 6, p. 27, 



plate 5, fig. 6. 

 Schizaster (Periaster) elongatus Guppy, 1882, Scientific Assoc. Trinidad, Proc, part 12, p. 196. 



The following is an extract from the original description of this species : 



The test is of medium size, elongate, hollowed, and expanded anteriorly; 

 subacuminate posteriorly. Upper face high, swollen, strongly carinate 

 posteriorly, having its greatest thickness a little behind the apical disk. 

 Posterior face subangular and truncate. Apical disk very excentric ante- 

 riorly. Anterior furrow wide, deep, commencing at the apical disk and 

 extending as far as the ambitus. The anterior ambulacrum III is different 

 from the others, with small pores separated by a granuliform swelling and 

 disposed in crowded pairs. The paired ambulacra are petaloid, subflexuous, 

 strongly excavated, and very nearly equal in length. The anterior am- 

 bulacra II and IV are very divergent [at an angle of about 165° to each 

 other], nearly horizontal; the posterior I and V more converging, forming 

 between them an acute angle [of about 40°]; poriferous areas are wider 

 than the interval between them, with pores which are equal, transverse, 

 elongate, and united by a furrow. The interambulacral areas are crowded, 

 compressed, very prominent at the approach to the summit. Tubercles 

 are abundant, small, unequal and scattered; the largest are in the anterior 

 region on the border of the ambulacral furrow. The peristome, periproct, 

 and apical disk are not visible in the only known specimen of the species. 



The height can not be given exactly, as the base of the specimen is 

 buried in matrix, but it is estimated to be about 18 mm., the length is 

 about 34 mm., the width 24 mm. While these measurements differ 

 markedly from those given by Cotteau, I think there is no question that 

 this is the specimen he figures, for he says that it is very rare, and the 

 specimen is buried in matrix in the same way that he delineates. The 

 species is distinguished from its near allies by its elongate form, apical 

 disk excentric anteriorly, deep and wide anterior furrow, and the paired 



