154 



THE VOYAGE OF H.M.S. CHALLENGER. 



The outline is somewhat more elliptical (PI. XXIX. " figs. 1, 5, 9), and the actinostome 

 more excentric than in older specimens ; the proportions of the coronal plates do not 

 differ materially in these younger specimens from those in the larger specimens, the 

 greatest disproportion being of course in the comparative size of the primary tubercles, 

 especially on the actinal surface. In the abactinal system in the largest of the young 

 specimens figured, the only difference in the arrangement of the apical plates is, that the 

 madreporic body has not yet encroached upon the plate separating it from the posterior 

 lateral genital plate (PI. XXIX." fig. 12'), and that the accessory plates separating the 

 genital plates from the anterior ambulacral areas are proportionally not as large as in the 

 largest specimen (PL XXIX.'' fig. 14), so that the ocular plates are comparatively nearer 

 together. In a still younger specimen, measuring only 22 mm., the apical system showed 

 the small intercalated plates between the anterior genital, and the termination of the 

 odd ambulacrum (PI. XXIX.* fig. 11'). Although the apical system is thus generally 

 identical, there is great variation in specimens of different sizes, in the relative size of the 

 genital plates, and the development of the intercalated plates. 



In all these younger, more elliptical stages, the ambulacral areas are somewhat 

 broader in proportion to their height (PI. XXIX.'' figs. 1-12) ; than in such a large fully 

 developed specimen as that figured on Plate XXIX.** figs. 1-4. 



On the actinal side in these young specimens, we find the plates of the ambulacral 

 and interambulacral areas more uniform in size ; they do not become elongated towards 

 the ambitus as do those of older specimens (PI. XXIX.'' figs. 3, 6, 10). 



Station 146. December 29, 1873. Lat. 46° 46' S., long. 45° 31' E. 

 bottom temperature, 1'5° C. ; globigerina ooze. 



Station 147. December 30, 1873. Lat. 46° 16' S., long. 48° 27 E. 

 bottom temperature, 0"8° C. ; globigerina ooze. 



Station 158. March 7, 1874. Lat 50° 1' S., long. 123° 4' E. ; 

 bottom temperature, 0'3° C. ; globigerina ooze. South Australia. 



Station 296. November 9, 1875. Lat. 38° 6' S., long. 88° 2' W. ; 

 bottom temperature, 1'2° C. ; red clay. 



Station 299. December 14, 1875. Lat. 33° 31' S., long. 74° 43' W. 

 bottom temperature ; 1-1° C. ; grey mud. 



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

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



1375 fathoms; 

 1600 fathoms ; 

 1800 fathoms ; 

 1825 fathoms; 

 2160 fathoms; 

 1375 fathoms; 



*Calymne. 

 Calymne, "Wy. Thomson, 1877 Voyage of the Challenger, Atlantic, vol. i. p. 397. 



Among the Echinids described by Thomson in his Voyage of the Challenger, vol. i. 

 p. 397, figs. 102, 103, the present genus holds, like Cystechiniis, an intermediate position 



