REPORT ON THE ECHINOIDEA. 99 



of the others figured in the same attitude. The test of Pliormosoma luculentum is far 

 more rigid than that of many of the species of the family, so that with its stifi" flattened 

 actinal surface it clearly shows a rounded ambitus and a somewhat conical outline as in 

 Plate IX. fig. 2. 



In a species of PJior-mosoma closely allied to Pliormosomxi placenta and Phormosoma 

 luculentum, which frequently came up in the dredgings of the "Blake" during the expedition 

 of 1878-79, the outline of the test when seen in profile was somewhat like the figure 

 of Plate IX. fig. 2, only the abactinal surface was more globular, and the flattened actinal 

 surface even sometimes bent upwards towards the edge near the ambitus. Still, in aU 

 these specimens of Phormosoma there was a very decided contrast between the flattened 

 actinal surface and the comparatively high globular abactinal surface. 



In the species of Asthenosoma, on the contrary, there was no such contrast between 

 the actinal and abactinal surfaces, the outline being in living specimens when seen in profile 

 nearly globular, as if the test had been blown up like a football. This is seen in 

 specimens which came up from moderate depths near 100 fathoms, and in which no 

 difierence of pressure would account for such excessive expansion. 



The very difierently shaped coronal plates composing the test of Phormosoma, near 

 the actinostome, in the outer half of the actinal surface, and on the abactinal surface of 

 the test (PI. X.* figs. 3, 4), as well as the striking difierence in the course and arrange- 

 ment of the poriferous zone on the two sides of the test, plainly show how hazardous it 

 is among the Palseechinidse to multiply the genera and species allied to Archceocidaris 

 and Pholidocidaris on structural features found combined in one and the same 

 species of the recent Echiuothuridse. In this species of Phormosoma {P. luculentum), 

 the fiat intertubercular space between the deeply sunken areolas of the primary spines 

 is broad, and does not form as in Phormosoma bursarium the weU-defined ridge so 

 characteristic of that species which recalls so strongly a similai- structural feature in 

 ArchcBOcidaris. 



Station 200. October 23, 1874. Lat. 6° 48' N., long. 122° 25' E. ; 255 fathoms; 

 mud. 



Station 205. November 13, 1874. Lat. 16° 42' K, long. 119° 22' E. ; 1050 

 fathoms; bottom temperature, 2-4° C. ; grey ooze. 



Station 191. September 23, 1874. Lat. 5° 41' S., long. 134° 4' E. ; 800 fathoms; 

 bottom temperature, 3 '9° C. ; mud. 



*Phormosoma bursarium, n. sp. (PI. X.''). 



I was inclined at first to consider the specimens on which I have distinguished this 

 species as belonging to Phormosoma luculentum, and to regard them as younger specimens. 

 On a re-examination, and after a careful study of the younger stages of the difierent 



