aENEEA ANH GEOUPS OF THE ECHTNOIUEA. 247 



openings. Madreporite extending backwards and separating 

 the posterior radial plates. 



Odd ambulacrum flush with the test, its pores exceedingly- 

 small. Lateral ambulacra short, sunken, subpetaloid ; pores large 

 and the poriferous zone broader than the interporiferous. Pos- 

 terior ambulacra the longest. Ambulacra wide around the peri- 

 stome and on either side of the actinal plastron. 



Peristome broad, excentric in front, with a large posterior lip. 

 Periproct bigh in the posterior extremity. Actinal plastron 

 amphisternous, long, and prolonged posteriorly into a short beak, 

 keeled along the median line. Three fascioles — a peripetalous, 

 an anal, and an independent subanal fasciole. 



Tubercles very small and numerous dorsally, and larger and 

 with a raised scrobicular surface actinally. Large tufted ambu- 

 lacral tubes close to the peristome. Spiues small, curved. 



Hecent. China, Tahiti, shores of Beluchistan. 



There is no doubt about the sunken nature of the lateral and 

 posterior ambulacra in the species from the Pacific and Indian' 

 Seas, and that the outer terminations of the petals of the am- 

 bulacra are prevented from closing by the peripetalous fasciole. 

 The madreporite is large and separates the basals, and extends 

 backwards well into the interradium. Now none of these cha- 

 racters occur in a species which A. Agassiz refers to BMnohrissus 

 with an expression of doubt (Report on the ' Blake ' Echini, 1883, 

 p. 67). The figures given by Agassiz, pis. xxiii. and xxvi., show 

 a most interesting form which is well deserving of the pains its 

 describer took about its details and the relation which they bear 

 to ancient forms of Spatangoids. He considers that the species will 

 probably form the basis of a subgenus of Bhinohrissus which will 

 hold to it very much the same relation which Periaster holds to the 

 true species of Schizaster. But it must be said that the Caribbean 

 Sea is not the home of the genus, and that the immature forms 

 of the Indian species have the true generic characters given above 

 and that the Micraster-look is wanting in them. The genus is 

 not known in the fossil state, and the species B, pyramidalis^ 

 Agass., is not a variable one. It will be best to place the 

 Caribbean form near the genera Linopnetistes and Oionohrissus 

 and in a new genus, Neopnemtes (page 258). 



