Classificator i) Position o/" Heraiaster plongatu3. 227 



include the genus Leskia^ which was afterwards named Palceo- 

 stoma by Loven, and it belongs to the family Spatangidte. 



Leshiadce. — No distinct subanal or actinal plastron ; a 

 peripetalous fasciole, enclosing slightly sunken ambulacra, 

 which are petaloid. Anal system covered by a small number 

 of plates ; actinostome pentagonal^ covered by live converging 

 plates, flush with the actinal surface. 



Dr. Gray gave a very full diagnosis of his family (not 

 subfamily) Leskiadse in the Cat. Recent Echinida in the Coll. 

 of the Brit. Mus. pt. i. p. 63, and in consequence reduced the 

 length of the generic diagnosis in the same work. The date 

 of the genus of Gray is 1851, and it was first published in 

 the Ann. & Mag. Nat. Hist. 1851 (vol. vii.). The family is 

 diagnosed as follows : — 



Shell ovate, subglobose, thin ; vertex central ; lateral 

 ambulacra broad, petaloid, rather sunken, and separate from 

 each other ; the hinder lateral pair rather the shortest ; the 

 odd anterior ambulacrum is in a rather broad sunken groove, 

 rudimentary, with a single series of pores on each side, all 

 surrounded by a broad, rather sinuous, peripetalous fasciole ; 

 lateral and subanal fasciole none ; mouth anterior, round, on 

 a level with the rounded under surface, and covered with five 

 triangular converging valves ; plastron and subanal plate not 

 distinctly defined ; anus round, in the upper part of the 

 rounded posterior end, and covered with five triangular con- 

 verging valves, forming a cone, with small spicula in the 

 centre ; ovarial pores two, very large ; spines and tubercles 

 subequal, subulate, those of the back being rather the largest. 



As the genus Leskia (subsequently Palceostoma) was the 

 only one of the family. Dr. Gray did not give a special generic 

 diagnosis, but contented himself with stating that the genus 

 has the characters of the family. 



He remarks, " This genus agrees with Brissus in the form 

 of the peripetalous fasciole, but differs from it and all other 

 Spatangidas in the form of the mouth and vent." He mentions 

 the species Leskia mirahilis, and states that the test is ovate 

 and feubglobose. Dr. Gray gave two drawings of the species 

 (Cat. Echin. Brit. Mus. &c., pi. iv. fig. 4), and the delinea- 

 tions carry out the idea given in the descriptions ; the absence 

 of a definite plastron, and the generally rounded form of the 

 under part are evident ; but the drawing conveys the impres- 

 sion that the peristome is not round, but pentagonal. The 

 upper surface of the test presents posteriorly a shallow groove, 

 in which is the anal opening with its plates. By \yay of 

 contrast Dr. Gray placed a figure of the under surface of 

 Kleinia luzonica below that of his Leskia, and the well- 



18* 



