REPORT ON THE ECHINOIDEA. 91 



New Britain, a very remarkable Astroijyga which he calls Astropyga elastica; unfortunately 

 it is as yet not figured, but, judging from his description, it is closely allied both to 

 Asthenosoma and to Astropyga ; the coronal plates of the tests resembling in structure 

 those of Asthenosoma, whUe the facies of the species and the arrangement of the spines 

 recall Astropyga radiata. This species was not collected by the Challenger, but some 

 of the young specimens of Echinothuridae which have been provisionally named may 

 ultimately prove to belong to this ty^a ; perhaps the young I have temporarily referred 

 to Asthenosoma gracile from Stations 184 and 219. The differences to be observed in the 

 structure of the test and arrangement of the spines in the figures of the young specimens 

 called Asthenosoma gracile and the normal Asthenosoma and Phormosoma are quite 

 striking when we compare them with the figm'es of an undoubted young Asthenosoma 

 {A. pellucidum) and of a genuine Phormosoma {P. tenue). 



Station 219. March 10, 1875. Lat. 1' 50' S., long. 146° 42' E.; 150 fathoms ; mud. 



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

 mud. 



Station 184. August 29, 1874. Lat. 12° 8' S., long. 145° 10' E.; 1400 fathoms; 

 bottom temj)erature, 1"8° C. ; grey ooze. 



Station 169. July 10, 1874. Lat. 37° 34' S., long. 179° 22' E. ; 700 fathoms; 

 bottom temperature, 4 "2° C. ; grey ooze. 



Phormosoma. 



Phormosoma, Wy. Thorn., 1874, Echin. Porcup., Trans. Eoy. Soc, vol. clxiv., part 2, p. 732. 



*Phormosoma tenue (Pis. XIII., XIV., XVII.^ fig. 8 ; PL XVIII. figs. 7-9 ; PL 

 XVIII.'' figs. 1-13; Pis. XVIII.^ XVIII.^ figs. 5-9; PL XIX. figs. 7-9; PL XIX." 

 fig. 2 ; PL XXXVIII. fig. 5 ; PL XXXIX. fig. 9 ; PL XL. figs. 29, 30 ; PL XLII. fig. 7 ; PL 

 XLIV. figs. 19-24). 



Phormosoma tenuis, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 202. 



In a large specimen (PL XIII. fig. 1) measuring 133 mm. in diameter, the primary 

 tubercles (when seen from the aljactinal side) are small and irregularly distributed over 

 the whole of the abactinal surface both in the ambulacral and interambulacral areas ; these 

 tubercles carry slender, hollow, cylindrical spines tapering but little at the extremity, the 

 intertubercular space is occupied by a few distant miliaries and secondaries carrying small 

 sharp spines. Immediately on the edge of the test are seen a few of the large primary 

 tul^ercles which on the actinal surface occupy the outer edge of the test and are arranged 

 in vertical rows, diminishing very rapidly in size as they approach the actinostome 

 (PL XIX.* fig. 2). The spines of these large tubercles are cylindrical, hollow, and a few 

 of them surmounted by a short conical hoof. These large spines are far less prominent 

 than in such species of the genus as Phormosoma hoplacantha, Phormosoma lucidentum, 



