274 PEor. p. M. dtjkcan's bevision or the 



The ambulacra are flusli with the test, apetalous, and the five 

 or six plates nearest the apex are small, in a single series ; lower 

 down and to the peristome there is a double series of ambulacral 

 plates. There is but one pore to a plate except at the peri- 

 stomial edge, where there are two in some plates. A subcircular 

 subaual fasciole only. The internal plates 6, 7, 8 of the broad 

 bivium are elongate and are within the episternal angle in 

 relation to the fasciole, and plates 7 and 8 have their pores 

 transposed to the episternal side of the suture. Phyllodian 

 tentacles with a single marginal row of filaments. Tubercles 

 small, several on a plate, largest actiually. 



Peristome widely open, more or less semilunar, with a small 

 labrum. The second and third plates of zone a in the right 

 posterior interradium are fused. An amphisternum, and the epi- 

 sternum is symmetrical and well developed. The periproct is 

 oval, longitudinal, placed towards the middle of the posterior 

 face, and it is comprised within the first five abdominal plates, 

 being separated from the episternum by one double plate only. 

 Oral and periproctal membrane-plates well developed. 



Recent. Azores, 250 fms. ; Caribbean Sea, 82-242 fms. ; be- 

 tween Bermuda and mainland, 233 fms. ; Philippines, 375 fms. 



The typical species is P. Josephince, Loven. 



The interesting type of this genus was dredged off the Jose- 

 phine Bank, and it measured eleven millimetres. It was doubt- 

 less immature, and upon the admission of that supposition 

 changes will probably have to be made in the diagnosis. Other 

 specimens of Palceotropus JosepMnce, Loven, have been discovered 

 in the Caribbean Sea; and A. Agassiz wrote upon them in the 

 * Blake ' Expedition, Eeport on the Echini, p. 53 (1883). A small 

 specimen 10 millim. in length did not differ from that figured by 

 Loven. 



Older specimens measuring 23 millim. in length (plate 

 xxiii.) are comparatively less globular and more flattened, but 

 otherwise do not vary greatly in appearance from the younger 

 specimens. 



A. Agassiz remarks that there is little difference in the 

 arrangement of the ambulacral plates in young and old speci- 

 mens ; but he figures the ambulacra of his specimens with double 

 plates near the apex. There are only two generative pores in all 

 the types, and Agassiz remarks on the presence of the basal 5. On 

 comparing the drawings of Falceotropus Josephince in the ' Blake 



