554 " THETIS " SCIENTIFIC UESULTS. 



Though completely crushed and otherwise in bad condition, 

 there is no doubt as to the identity of this specimen. According 

 to Etheridge, ^'^ who gives an interesting account of its habitat 

 and habits, it is fairly common on Lord Howe Island, but is not 

 abundant. 



CH^TODIADEMA TUBERCULATUM.^^e gp. nov. 



(Plates Ivi. and Ivii.) 



Test strongly flattened ; vertical diameter (15 mm.) only about 

 •27 of horizontal (55 mm.); coronal plates about 16, uppermost 

 four without primary tubercles; next two, each with one near 

 outer end ; those just above ambitus with two or three ; tliose at 

 ambitus and just below with three or four; remaining actinul 

 interambulacral plates with A'ery small primary tubercles or none; 

 above ambitus, secondary tubercles of interambulacra lew, 

 scattered and confined almost wholly to outer end of plates; 

 becoming more numerous and more generally distributed at 

 ambitus, they increase rapidly actinally and completely cover the 

 surface of the lowermost coronal plates ; miliary tubercles fairly 

 abundant on actinal surface, but comparatively infrequent 

 abactinally. Ambulacral areas rather narrow (9 mm.), about one- 

 third as wide as interambulacra (28 mm.); uppermost two or 

 three ambulacral plates without primary tubercles, but all others 

 above and at midzone carry one each ; below midzone only 

 secondary and miliary tubercles are present, but these completely 

 cover the surface of the plates. Pairs of pores in distinct arcs 

 of three at and above midzone, but below midzone apparently 

 only two pairs, or even a single pain, to each plate, and these are 

 widely separated, and form a straight series ; from actinostome 

 to ambitus there are about twenty pairs of pores on each side of 

 each ambulacrum. Primary tutiercles of both ambulacra and 

 interambulacra perforate and decidedly crenulate. Abactinal 

 system 19'5mm. in diameter ("SSlLd.), with all the oculars 

 broadly insert. Genital and ocular plates each with three or 

 four secondary tubercles. Centre of periprocb occupied by anal 

 tube and a surrounding zone of very minute plates, outside of 

 which is a zone of plates 1 — 3 mm. in diameter, each carrying a 

 secondary or miliary tubercle, Actinostome very small, 10 mm. 

 in diameter (-ISh.d.), with very distinct but rather wide actinal 

 cuts; buccal membrane sparsely covered by minute plates, some 



33 Etheridge— Austr. Mas. Mem., ii., 1, No. 1, 1889, p. 37. 



3 6 iu6erc«Zum — a tubercle + a<MS = possessing, in reference to the actinaL 

 surface having distinct tubercles, instead of being closely granulated as in 

 C. gramilatuin, Mortensen. 



