280 PROP. p. M. DUNCAN'S EETISION OF THE 



A deep anterior recess with the peristome vertical and at its 

 lowest part. The periproct superior to the projecting posterior 

 rostrum, or when there is no rostrum, placed actinally. Apical 

 system variable, compact or disconnected. Ambulacra flusb, 

 apetalous, may be disconnected or discontinuous ; pores single or 

 slit-like. Tentacles homoiopodous. Interradia forming, or not, 

 a continuous vertical band in the postero-lateral areas ; sternum 

 distinct or not. Spheridia absent in the anterior ambulacrum 

 and exposed and numerous in the others. A subanal fascicle 

 may or may not exist, but is not accompanied by modification of 

 the ambulacral plates. Spines short, straight or curved, only 

 crowded on the sternum. 



Genus Pourtalesia. 

 Spa tagocystis. 

 Echinocrepis, 



The genus Pourtalesia, A. Agassiz, is one of the most inter- 

 esting, and its afiinities have given much trouble to the three 

 distinguished naturalists to whom we owe the knowledge of the 

 morphology of the species. The first species, P. miranda, which 

 was used as the type of tbe genus by A. Agassiz, was dredged by 

 the late M. de Pourtales off" Florida, at a depth of 349 fathoms, 

 and it was described by A. Agassiz, 1869, in Bull. Mus. Comp. 

 Zool. i, p. 272. Subsequently the genus and the same species, 

 P. miranda, were described in the 'Eevision of the Echini,' 1872- 

 74, p. 344, pi. xviii. The dredgings of H.M.S. 'Porcupine' 

 yielded two other species, which were described by the late Sir 

 "Wyville Thomson in Phil. Trans. 1874, p. 747, pis, Ixx. and Ixxi. 

 These species, P. Jeffreysi and P. pTiiale (P. phi/ale, "W. T.), 

 were got — the first-named from 317 fathoms between Faroe and 

 Shetland, and the latter from 1215 fathoms in the Eockall Channel. 

 An excellent general description of P. Jeffreysi and a very good 

 engraving were published by the same author in his work called 

 ' The Depths of the Sea,' 1873, p. 108. 



The dredgings of the ' Challenger ' in the Pacific produced no 

 less than five new species, and they were described and figured 

 in the Eeport on the Echinoidea by A. Agassiz, 1881, p. 132 

 — P. carinata, P. Jiispida, P. laguncula, P. ceratopyga, and P. 

 rosea. The genus has its principal quarters in the Pacific Ocean, 

 where there are five species ; and there are three species in the 

 Atlantic, viz. P. Jeffreysi, P. phiale, and P. miranda. These are 



