110 PAXAMIC DEEP SEA ECHINI. 



Young specimens of 9 mm. carry spheridia on the second buccal plate 

 (PI. 43, fig. 3). Spheridia are usually found on the actinal coronal plates 

 in Ph. placenta; in an Asthenosoma pelhieidum of 34 mm. we find spheridia 

 on the ambulacral plates in process of passing over to the actinal system 

 (PI. 51, fig. 5). In addition, on the actinal surface nearly to the ambitus the 

 half plates all carry spheridia (PI. 51, fig. 7). In Asthenosoma coriacemn 

 spheridia are found nearly up to the ocular plate on the posterior zone of the 

 left posterior ambulacrum (PI. 52, fig. 1). 



Kamptosoma Mort. 



Kamptosoma Mortenseii, The Danish " Ingolf " Expedition. Echinoidea, Part 1., p. 60, 1903. 



A few specimens of Echini collected by the " Challenger," were left 

 in Cambridge, and were not returned to Sir Wyville Thomson with the rest 

 of the collection, owing to my ill health and the death of Count Pourtales. 

 Among them was a specimen labelled "Ph. tenue?" from Station 272.' 

 The peculiar features presented by this specimen led me to examine it 

 again. I soon discovered that it differed greatly from Pkormosoma tenue, 

 and that it, as well as Ph. asterias, should form a new genus of Echinothurise. 

 I came to this conclusion in 1898, at the time I was writing the Preliminary 

 Report of the Echini of the '-Albatross" Expedition of 1891; at that 

 time the sketch notes, which have since been drawn out carefully by Mr. 

 Westergren, were made (PI. 50). In 1903 Dr. Mortensen published the 

 results of an examination he made of another specimen of Ph. tenue? from 

 the same locality, and called attention to the interesting structure of the 

 ambulacral system of Ph. tenue and of Ph. listerias;- and proposed for these 

 two species the genus Kamptosoma. 



Kamptosoma indistinctum A. Ag. 



Phormosoma tenue A. Ag. pars., "ChalleDger '' Echinoidea, 1881, p. 91. 



Plate 50. 



In a specimen of 42 mm. in diameter, from "Challenger" Station 272, 

 the actinal system (PI. 50 fig. J), measured 9 mm. in diameter, and the 

 abactinal system 12 mm. In no genus of Echinothurise is the contrast 



1 In 2600 fathoms, in Lat. 3° 18 S. and Long. 15"2° 56' W., east of Maiden Isd. ; bott. temp. 1°C. 

 - " Challenger " Station 299. On the way to Valparaiso from Juan Fernandez, in 2160 fathoms. 



