REPORT ON THE ECHINOIDEA. 103 



Station 300. December 17, 1875. Lat. 33° 42' S., long. 78° 18' W. ; 1375 fathoms ; 

 bottom temperature, 1*5° C ; giobigerina ooze. 



Station leia. June 13, 1874. Lat. 34° 13' S., long. 151° 38' E. ; 410 fathoms; 

 grey ooze. 



Station 235. June 4, 1875. Lat. 34° 7' N., long. 138° O' E. ; 565 fathoms ; bottom 

 temperature, 3"3° C. ; mud. 



*Pho7-mosoma uranus (PI. XVIIL" fig. 12). 



Phm-mosoma uranus, Wy. Thomson, 1877, Voyage of the Challenger, Atlantic, vol. i. p. 146, 

 fig. 33, p. 147, fig. 34. 



Thomson has figured in the Voyage of the Challenger (vol. i. p. 146, fig. 33, p. 147, 

 fig. 34), a species of Phormosoma difiering greatly from that collected by the Porcupine 

 and named by him Phormosoma placenta (Trans. Eoy. Soc, 1874, vol. cLxiv. part 2, p. 732, 

 Pis. Ixii. Ixiii.) ; the latter species was remarkable for the large tubercles of the 

 actinal surface occuppng with their areolas the greater part of the ambulacral and inter- 

 ambulacral plates. The present species is more closely related to Phormosoma tenue, in 

 -which the large tubercles are not closely packed but irregularly arranged and limited to 

 a comparatively narrow edge of the abactinal surface immediately adjoining the ambitus. 

 It differs also from specimens of Phormosoma tenue in the arrangement of the poriferous 

 zone, which is well shown by Thomson on fig. 34 ; the intercalated ambulacral plate 

 is proportionally large and still extends to the outer edge of the ambulacral area, the 

 poriferous zone thus forming a nearly vertical line (somewhat irregular) of pores 

 extending from the actinal opening to the abactinal area ; the species holds, as Thomson 

 has noticed, an intermediate place between Phormosoma and Asthenosorna. 



The extreme tenuity of the test of this species is very remarkable, the coronal plates 

 of the abactinal area of the only specimen collected are so thin that the test can be rolled 

 up without injury to the specimen. The shape of the plates of the ambulacral zone on 

 the abactinal side at once distinguish this species from Phormosmna tenue, in which the 

 corresponding plates are comparatively narrower, while the primary ambulacral plates of 

 Phorraosoma uranus are fully as high as the corresponding interambulacral plates. This 

 is not the case in Phormosoma tenue (see PI. XIV. fig. 1). 



Among the Echinoidea dredged by the last "Blake" expedition there are a number of 

 specimens of a species closely allied if not identical to Phormosoma uranus ; as these are 

 of all sizes I may be able to ascertain how far the characters which I have used to 

 distinguish Phormosoma uranus and its Pacific representative are constant. 



Stttion 6. January 30, 1873. Lat. 36° 23' N., long. 11° 18' W. ; 1525 fathoms; 

 bottom temperature, 1 "6° C. ; giobigerina ooze. 



Station 78. July 10, 1873. Lat. 37° 24' N., long. 25° 13' W. ; 1000 fathoms; 

 giobigerina ooze. 



