148 THE VOYAGE OF H.M.S. CHALLENGEE. 



this specimen to be an exaggeration of some of the younger stages (PL XXX. figs. 6, 7), 

 which show a very marked tendency towards a high conical test. The specimen figured 

 on Plate XXX.^ figs. 1-5 has, like the younger stages, only one large well-developed 

 primary tubercle on each coronal plate of the abactinal part of the test. This abnormal 

 specimen of Urechinus 7iaresianus shows how close is the afiinity between Urechinus 

 and Cystechinus, and that we may have in these genera fully as great a difi"erence in the 

 outline of the test as we find in any of the species of Ananchytes from the Chalk. 



The colour of the test in alcohol varies from a dirty yellow to a dark brownish-red. 



Station 146. December 29, 1873. Lat. 46° 46' S., long. 45° 31' E. ; 1375 fathoms; 

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



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

 fathoms ; bottom temperature, 0'8° C. ; globigerina ooze. 



Station 158. March 7, 1874. Lat. 50° 1' S., long. 123° 4' E. ; 1800 fathoms; 

 bottom temperature, 0"3° C. ; globigerina ooze. 



Station 302. December 28, 1875. Lat. 42° 43' S., long. 82° 11' W. ; 1450 

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



* Cystechinus. 

 Cystechinus, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. i). 207. 



This genus has the facies of Ananchytes, and is also closely allied to Galerites. 

 It has, like the latter, the test made up of plates of nearly uniform size in the different 

 interambulacral areas, and large plates like the Ananchytidse in the ambulacral areas, 

 and a slightly sunken actinostome. In this genus the actinostome is less eccentric than 

 is usual in Spatangoids, and in this respect one of the Galeritic features of the genus is 

 strongly marked. The anal system is just below the ambitus, but it has the abactinal 

 system of the Ananchytidse. It, however, forms a most interesting genus, and with 

 Pourtalesia, which was first described from the dredgings of Mr Pourtales and the allied 

 genera Palceotropus, Neolampas, and the like, shows the affinities of the Spatangoids 

 with the Echinolampadse. 



It has, like aU Pom-talesiae, simple ambulacral pores. It is remarkable how the 

 structure of so many of the Spatangoid forms is satisfactorily explained by the different 

 genera of Pourtalesise collected by the Challenger, and how greatly the knowledge of the 

 members of this family has helped us to understand the true relationship, not only of 

 many aberrant groups of Spatangoids, Ijut also their relationship to the Clypeastroids 

 and Echinolampadse. 



In addition to the proportions of the coronal plates in the ambulacral and inter- 

 ambulacral areas, the rudimentary auricles, the raised edge of the actinal opening 

 described in the following species are points specially interesting. 



