52 URECHIXUS XARESIANUS. 



Pourtalesia miranda A. Ag. 



Off Havana, Grenada. 242-57G fathoms. 



The fragments of other Pourtalesise, dredged principally off the Barbados, 

 to which I referred in Bull. M. C. Z., VIII., No. 2, p. 80, 1880, belong prob- 

 ably to the genera Cystechinus and Spatagocystis. The fragments are too 

 imperfect for determination, and have no value beyond the fact that they 

 indicate the presence of other species of the group in the West Indies. 



Urechinus naresianus A. Ag. 



Lesser Antilles, Lat. 41° 24' 45" N., Long. 65° 35' 30" W. 422-1242 fathoms. 



PI. XXVI. Figs. 1-3. 



The greater part of the specimens collected by the Blake measured 

 about 30 mm. in length, but varied greatly in height. Tbey agree quite 

 closely with what I have designated as the normal stage in the Report of the 

 Challenger Echini. (See Chall. Ech., PI. XXX a . Figs. 7-9, p. 146.) Tbe 

 specimens examined all show but three genital openings. The structure of 

 the subanal fasciole shows that in this genus it assumes all the stages of de- 

 velopment intermediate between a well-defined subanal plastron, such as is 

 figured on Plate XXX\ of the Challenger Echini Report, and a stage in 

 which this fasciole is indicated merely by irregular accumulations of mili- 

 ary tubercles. So that tbe genus Urechinus is the representative of the 

 oldest Spatangoids with a disconnected apical system, large ambulacra] and 

 interambulacral plates with simple linear ambulacral pores, in which the 

 subanal fasciole (the only one existing) is still in process of formation ; this 

 type of Spatangoid leading us little by little to Spatangoid genera in which 

 the ambulacra become more or less petaloid, as in Homolampas, Paleopneus- 

 tes, and the like, till we get the modern type of Spatangus proper, with 

 well-defined petaloid ambulacra, and a highly developed subanal fasciole, 

 the lateral fasciole existing in some of these genera, Paleopneustes, Lino- 

 pneustes, Calymne, Maretia, etc.. in a rudimentary form, as accumulations of 

 miliary tubercles along tbe ambitus. On tbe other hand, a slender peripeta- 

 lous fasciole is in some genera. Paleopneustes, Homolampas, Rhinobrissus, 

 etc., developed as a slender thread, or as a more or less well-defined fasciole 

 extending across the termination of the more or less rudimentary petals. 



We find the lateral fasciole developed from the peripetalous fasciole in 



