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



Echinidse, of such forms as Echinus miliaris, but the opening of the actinostome is 

 comparatively larger. In all the buccal plates the tentacle of one of the pairs is rudi- 

 mentary or even wanting (PI. VI.^ fig 12). The test is thin, much as in the Salmacidae, 

 and it has as well as the spines a silvery lustre as in Trigonocidaris. The coronal plates 

 are high ; the pairs of large pores are arranged in a single vertical row. 



The anal system is large, but still covered with a few large plates as in all young 

 Echinidse (PL VI.'* fig. 13). The genital plates are of uniform size ; the ocular plates are 

 notched in the apex of the ambulacral row, they are excluded from the anal system. The 

 primary tuberculation of the upper part of the test extends over the genital ring. The 

 pedicellariaj are numerous, especially above the ambitus ; they are all of tbe large-headed 

 slender-stemmed form. The most striking feature of this genus, however, is the structure 

 of the spines; thus far it was mainly among Cidaridse, Salenidee, Diadematid^, and 

 Arbacidae, that the spines differed greatly in shape, in closely allied genera, or even in the 

 species of the same genus. Among the Echinidse, though we find in very young specimens 

 marked serrations along the fluting of the spines, yet these disappear with age, forming a 

 more or less uniform fluting in all the Echinidee proper. In this genus, however, the spines 

 of the test are still prominently serrated in comparatively large specimens (PI. VI." 

 figs. 11, 11a), at least in specimens of a size which, in the young Echinid^ which have 

 been examined, have all the features of the adult. In addition to the serrations they are 

 also flattened (PI. VI.* fig. 11a), resembling to a considerable extent some of the spines 

 of Salenia varispina. What shape they assume in the adult will be interesting to dis- 

 cover. This genus is most interesting, as it is the first instance showing any relation- 

 ship in the shape of the spines, between the genera of the Echinidge proper, and the 

 Cidaridse and Salenidse, in addition to the common structural features of the actinostome. 

 This genus has also affinities to Trigonocidaris and others of the Salmacidse as stated 

 above. 



The test is flattened, the actinal cuts are slight; there is one large primary tubercle 

 on each coronal plate both of the ambulacral and interambulacral areas, forming in both 

 areas very distinct vertical rows ; the rest of the interambulacral plates carry small second- 

 aries irregulary arranged round the centrally placed primary (PI. VI."* fig. 14); in the 

 ambulacral area the primaries are near the median line, separated from the poriferous 

 zone by irregular arcs of secondaries. The poriferous zone is comparatively broad, the 

 pairs of pores well separated vertically. 



Station 164. June 12, 1874. Lat. 34° 8' S., long. 152° 0' E.; 950 fathoms; bottom 

 temperature, 2"2° C. ; grey ooze. 



Station 218. March 1, 1875. Lat. 2° 33' S., long. 144° 4' E.; 1070 fathoms; 

 bottom temperature, 2'1° C. ; globigerina ooze. 



Station 207. January 16, 1875. Lat. 12° 21' N., long. 122° 15' E; 700 fathoms; 

 bottom temperature, 10 '8° C. ; mud. 



