186 PANAMIC DEEP SEA ECHINI. 



Mr. Gregory 1 has established the genus Archeopneustes, with Paleop- 

 neustes kystrix A. Ag. as type, to include 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. hystrix the petals reach the 

 ambitus. They fall short of the ambitus, there bring 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 abaetinal side. The structure of the 

 petals of P. hystrix 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. 2 



Phrissocystis A. Ag. 



Phrissocystis A. Ag., Bull. M. C. Z. 1898, XXXII. No. 5, p. 80. 



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

 latter, pairs of pores piercing the abaetinal 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 Palaeotropus and the 

 Ananchytid genera Cystechinus, Calymne, 

 Urechinus, and the like, while in Palseobrissus 

 the small narrow ambulacral plates with pairs 

 of pores extend well towards the ambitus. 

 The actinostome, however, is eminently Spa- 

 tangoid, the labium and the phyllodes take a 

 Fig. 276. Phbissocystjs acci.eata. great development, much as they do in Pa- 



leopneustes 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 tuberculatum 

 both of the ambulacral and interambulacral areas recalls that of Paleop- 

 neustes. On the actinal side the posterior plastron is greatly developed, 



1 Q. J. Geo]. Soc. London, May. 1892, XLVHI, p. 163. 



a Echiuides . . . du S. Y. " Belgica," p. 12, Pis. V, fig. 37; VI, figs. 42, 43. 



