Corals dredged by H.M.S. ' Challenger. 3 553 



tint — not white as in D. Agassizii. In the structure of the columella 

 this species differs more strongly than D. Agassizii from D. italicus, the 

 columella being very diffuse and finely trabecular, whilst there is no trace 

 of the rows of tubercles on the costse. A fifth cycle of septa is fully 

 developed, whereas the other two species of the genus have only four 

 cycles. All the septa bear pali disposed in four crowns, the quaternary 

 pali being largest. The diameter of the corallum is 3 centims. The 

 disk of the living animal was of a light ochre-yellow colour, somewhat 

 reddened towards the margin of the calicle. The tentacles were white. 



Platytroclius rubescens, sp. n. 



The corallum is compressed and wedge-shaped, without trace of ad- 

 herence, and provided with lateral aliform expansions derived from the 

 lateral costae. It has six systems of septa and four cycles. The septa 

 are exsert with rounded superior borders. The columella is elongate 

 and fascicular. The corallum is of a pale reddish colour. In outward 

 aspects this coral resembles the genus Endopachys *, but shows no trace 

 of perforate structure. It appears also related to the genus SpJieno- 

 trochus f , in which, however, there are only three cycles of septa, and the 

 septa are not exsert. Sphenotrochus crispus has the lateral costse more 

 developed than those of the faces. It is placed provisionally in the 

 genus Platytroclius, which, however, has in the species known only three 

 cycles of septa. The Platytrochi have broad, lateral costse. PI. Stolcesii 

 was placed by Lonsdale in his genus Endopachys. Several living speci- 

 mens and two dead ones of PI. rubescens were obtained from 129 fathoms 

 off the Ke Islands. 



Ceratotrochus diadcma, sp. n. 



The corallum is white ; it is shallow and saucer-shaped ; it has a 

 short, rudimentary pedicle, with small scar of adherence. The primary 

 and secondary costse are prominent and serrate. There are six systems 

 of septa and five cycles. The whole of the septa are exsert, the 

 primary and secondary extremely so, projecting 1 centim. above the 

 margin of the calicle. The quinary septa unite with the quaternary, 

 the quaternary with the tertiary, and the tertiary with the secondary. 

 The primary septa remain free throughout their whole course to the 

 columella. The columella is large and oval, and composed of contorted 

 fascicular matter. 



The extreme diameter of the corallum between the tips of the exsert 

 septa is 5-75 centims,, the extreme height 2-15 centims. 



A young specimen of this coral, with the soft parts in situ, was 

 dredged on 10th July, 1873, in lat. 37° 26' N., long. 25° 14' W., from 

 1000 fathoms ; and a single adult specimen was obtained from off Per- 



* MM. Edwards and Hainie, I. c. t. iii. p. 97, 

 t Ibid. t. ii. p. 65, 



