NO. 4 ECHINOIDS, TRINIDAD AND VENEZUELA — COOKE 29 



RHYNOBRISSUS ROSTRATUS Cooke, n. sp. 

 PI. 14, figs. 1-4 



Horizontal outline pointed ovate, strongly rostrate behind; lateral 

 profile narrowly wedge shaped, highest behind ; posterior end slop- 

 ing downward and forward at an angle approximating 45°. Apical 

 system somewhat anterior, not preserved (the genus has four genital 

 pores, the posterior pair separated by the protruding madreporite). 

 Anterior ambulacrum flush, not at all petaloid. Petals depressed ; an- 

 terior pair forming a straight line, extending about three-fourths the 

 way to the margin, the anterior half much reduced in width near the 

 apical system ; posterior petals longer, straight, not widely diverging ; 

 pores oval. Peristome anterior, strongly lipped. Periproct bilunate, 

 transversely elongated, high on the rostrate end. Peripetalous fasciole 

 strongly depressed; slightly reentrant between the lateral petals. 

 Subanal and circumanal fascioles connected, forming a figure 8. 

 Tubercles small, close set and granular on the upper surface, larger 

 and farther apart on the lower surface. 



Length 51.4 mm. ; width 37.3 mm. ; height 24.5 mm. 



Occurrence. — Venezuela : Punta Gavilan, Falcon. 



Geologic horizon. — Miocene ? : Probably from the La Vela forma- 

 tion, of late Miocene age. 



Holotype. — Naturhistorisches Museum, Basel, Switzerland. 



Comparison. — The unique type of this species is somewhat dis- 

 torted by crushing. It most closely resembles Rhynohrissiis cuneus 

 Cooke (1959, p. 88, pi. 36, figs. 7-11), living off the coast of North 

 Carolina. It differs from R. cuneus as follows : Its anterior petals are 

 more widely diverging. Its posterior end is narrower, more rostrate, 

 more strongly overhanging. Its plastron is more protruding and less 

 nearly elliptical. Its periproct is nearer the junction of the anal and 

 circumanal fascioles, and its peripetalous fasciole is somewhat in- 

 dented. Some of these differences may be the result of distortion, the 

 others possibly are individual variations. If so, this species will fall 

 into the synonymy of Rhynobrissus cuneus. 



BIBLIOGRAPHY 



Agassiz, Louis. 



1841. Des scutelles. Monographies d'echinodermes vivans et fossilcs, Mon- 

 ogr. 2, 151 pp., 27 pis. 

 Anisgard, Harry W. 



1954 (1955). An echinoid from the Eocene of western Venezuela. Journ. 

 Paleont., vol. 28, No. 6, pp. 830-835, 5 text figs. 



