146 THE VOYAGE OF H.M.S. CHALLENGER. 



shallow. The test of this species is comparatively stouter than in the other genera of 

 the family. 



There were, unfortunately, only two specimens collected by the Challenger ; they are 

 figured natural size on Plates XXVII. and XXXV. '^ 



Station 147. December 30, 1873. Lat. 46° 16' S., long. 48° 27' E.; 1600 fathoms; 

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



* Urechinus. 

 Urechinus, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 207. 



At first sight this genus appears closely allied to Neolampas, of which it has the 

 general outline. The posterior region of the test forms as in that genus the 

 hood protecting the anal system. The difference in the proportion of the plates 

 composing the ambulacral and interambulacral areas as well as the structure of the 

 actinostome at once distinguish it from Neolampas. It has, like the Pourtalesise, large 

 high plates forming the ambulacral zones differing little in height from the adjoining 

 ambulacral plates. It has a nearly circular actinostome like that of Ci/stechimis slightly 

 sunken below the level of the actinal surface. The abactinal system is disconnected ; 

 two of the genital plates go with the trivium, the others with the bivium. 



''Urechinus naresianus (PI. XXIX figs. 1-4; Pis. XXX., XXX.^ figs. 1-14; PI. 

 XXXIX. figs. 29, 30 ; PI. XL. figs. 56-58). 



Urechinus naresianus, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 207. 



The largest specimens collected measured 48 mm. ; the test was of a reddish-brown 

 colour forming the ground- work upon which stood out in prominent contrast the delicate 

 slender primary spines with broad bases (PL- XXX. fig. 20), of a yellowish-white, as well 

 as the numerous minute secondary and miliary spines thickly crowding the whole test. 

 In these large specimens the primary tubercles remain comparatively large ; they are 

 never numerous, each primary coronal plate carrying but few ; they are more numerous on 

 the actinal side. In the younger stages, even when the specimens have attained 25 mm. in 

 length, each coronal plate was occupied by but a single primary tubercle both in the ambu- 

 lacral and interambulacral areas (PI. XXX. figs. 1-3), the rest of the plate being thickly 

 covered by miliaries and secondaries. The youngest specimens collected have akeady the 

 same general arrangement, and differ but little from the older specimens (PI. XXX. figs. 

 4-13) ; these are somewhat more elongated and more flattened; the anterior extremity 

 of the test when seen in profile (PL XXX. figs. 9, 13) being comparatively more gibbous. 



In all the stages examined the actinal surface was more closely tuberculated 

 than the abactinal region, the miliary and secondary sjjines forming a close 

 down over the whole of that surface. Seen from above the test is elliptical, slightly 

 tapering at the posterior extremity (PL XXIX. fig. 1 ; PL XXX. figs. 1, 4, 7, 8, 11). Seen 



