186 PANAMIC DEEP SEA ECHINI. 



Mr. Gregory ' has established tlie genus Archeopneastes, with Pakop- 

 neiisles hystrix A. Ag. as type, to inchide an interesting Spatangoid from 

 Bissex Hill, Barbados, from the uppermost limestone of the Oceanic Series. 

 Mr. Gregory is in error in stating that in P. hydrix the petals reach the 

 ambitus. They fall short of the ambitus, there being in the anterior ambu- 

 lacra four to five ambulacral plates between the ambitus and the termina- 

 tion of the petals, and a larger number in the posterior ambulacra, which are 

 still shorter. As there is no profile figured of P. hystrix, Mr. Gregory was 

 misled by the figures seen from the abactinal side. The structure of the 

 petals of P. Jtystrix is quite like that of P. cristatus, and has nothing in com- 

 mon with those of the fossil Archeopneustes of Gregory. His genus Archeop- 

 neustes seems to me more closely allied to Amphipneustes of Koehler.^ 



Phrissocystis a. Ag. 



Phiissocystis A. Ag., Bull. M. C. Z. 1898, XXXII. No. 5, \\ 80. 



This genus is allied to Palceotropus and Palseobrissus in having, like the 

 latter, pairs of pores piercing the abactinal ambulacral plates, they are, 



however, limited to the four or five or six 

 uppermost plates, where the pores become 

 simple, and where the ambulacra are all 

 equally developed, as in Pala?otropus and the 

 Ananch^tid genera Cystechinus, Calymne, 

 Urechinus, and the like, while in Palreobrissus 

 the small narrow ambulacral plates with paire 

 of pores extend well towards the ambitus. 

 The actinostome, however, is ennnently 8pa- 

 ,..„„„„ tangoid, the labium and the phyllodes take a 



Fig. 27C). I'iihissocysiis a( i i.eata. great development, much as they do in Pa- 



leoi)neustes and Linopneustes. The apical 

 system is compact, Fig. 276, as it is in the last named genera, and the long 

 curved primary spines recall those of the same genera. The tuberculation 

 both of the ambulacrnl and interainbulacral areas recalls that of Paleojv 

 neustos. On the actinal side the posterior plastron is greatly developed. 



' Q. .1. Geol. Soc. London, May, 1802. XLNUI. p. \m. 



'^ fichinides . . . du S. Y. " I^elgica," j.. IL'. I'ls. V. fig. 37; VI, figs. 42, 43. 



