REPORT ON THE ECHINOIDEA. 97 



and a large head, irregularly scattered among the others of the same kind as on the 

 abactinal side (PI. XVIII. * fig. 12). I have not found the peculiar tetradactyle pedicel- 

 larise (Echrnids of Porcupine, Trans. Eoy. Soc, 1874, pi. Ixvii. fig. 6) described by Thomson 

 as so characteristic of Phormosoma fenestratwn. In this species the ambulacral plates 

 perforated by the pores are larger than in Phormosoma placenta figured by Thomson. 



Phormosoma tenue and Phormosoma uranus are at once readily distinguished from 

 Phormosoma ])lacenta on account of the greater similarity in the structure of the actinal 

 and abactinal surface of the test. 



Station 274. Sept. 11, 1875. Lat. 7' 25' S., long. 152° 15' W.; 2750 fathoms; 

 bottom temperature, 0'9° C. ; radiolarian ooze. 



Station 237. June 17, 1875. Lat. 34" 37' N., long. 140" 32' E.; 1875 fathoms; 

 bottom temperature, 1'7° C. ; mud. 



Station 272. Sept. 8, 1875. Lat. 3° 48' S., long. 152° 56' W.; 2600 fathoms; 

 bottom temperature, 1'0° C. ; radiolarian ooze. 



*Phormosoma luculentum (Pis. IX., X., X." figs. 3-7 ; PI. XXXIX. fig. 8 ; PI. XL. 

 figs. 31-36 ; PL XLIV. figs. 25-27. 



Phormosoma luculcnta, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 201. 



This is perhaps the most striking of the Echinothuridse collected by the Challenger. 

 The test is of a beautiful light violet colour, forming a brilliant contrast to the white 

 lines (Pis. IX., X., X." figs. 3, 4) indicating the sutures of the coronal plates, to the 

 jet black or deep violet, long smooth shiny primary spines, and to the silvery white 

 hoofs tipping the large primary spines of the ambulacral and interambulacral areas 

 scattered here and there along the edge of the test, when seen from the abactinal side, 

 and projecting over the lower surface of the test when seen from the actinal side. This 

 species is marked by the long narrow coronal plates of the abactinal surface (PL IX. 

 ficr. 1 ; PL X." fig. 3), the small size of the few primary tubercles irregularly placed on the 

 abactinal side of the test near the ambitus, the narrow ambulacral system, and the narrow 

 poriferous zone. The abactinal surface of the test is covered by short, sharp miliary and 

 secondary spines, few in number, and irregularly placed on the plates, leaving the test 

 nearly bare, although pitted with numerous miliaries carrying no spines (PI. X.^ fig. 3). 

 On the actinal side the primary tubercles are large, and are arranged in three more or 

 less regular horizontal rows near the ambitus (PL X.* fig. 4) ; these tubercles are sur- 

 mounted by large hollow cylindrical spines tipped with truncated conical hoofs (PL X. 



fig. 1). 



The small secondaries scattered over the actinal surface carry short club-shaped or 

 pointed spines (PL X. fig. 1). The flat intertubercular spaces are filled by short, sharp 

 miliary spines closely packed together between the larger primaries near the ambitus, 



(ZOOL. CHALL. EXP.— PART IX.— 1881.) ^ 13 



