Prof. W. Thomson on the Deej^-sea Dredging-expeditions. 303 



scales, through which the ranges of double pores and ambulacral tubes 

 are continued up to the edge of the mouth as in Cidaris. The am- 

 bulacral plates are strap-shaped, and the pores trigeminal; the two 

 inner pairs of each arc pass through small accessory plates inter- 

 calated between the ambulacral plates, and the third pair, remote 

 from the others, pass through the end of the ambulacral plate. The 

 dental pyramid is broad and low, and the teeth are simply grooved as 

 in Cidaris. The two divisions of the tooth-socket are not united by a 

 closed arch ; the ambulacral tube-feet on the oral surface are provided 

 with suckers, while those on the apical surface are simple and conical. 



Phormosoma, n. g. 

 Plates overlapping slightly and forming a continuous shell, the 

 corona coming to a sharp edge at the periphery, and the upper 

 surface of body differing greatly in character from the lower. 



1 . P. placenta, n. sp. 



One example from 500 fathoms off the Butt of the Lews ; several 

 fragments from deep water in the Rockall Channel. 



Calveria, n. g. 

 Plates overlapping greatly in the middle line of the ambulacral and 

 interambulacral areee. Plates narrow, and leaving fenestrse between 

 them which are filled up with membrane. Character of the peri- 

 stome with regard to the distribution of spines, the structure of the 

 pore-arese, &c. nearly uniform from the apex to the edge of the peri- 

 stome. 



1. C. hystrix, n. sp. 



Fenestrse between the plates small. Colour a nearly uniform rich 

 claret. One specimen in deep water off the Butt of the Lews. 



2. C.fenestrata, n. sp. 



Plates narrower than in the last species, and fenestrse wider. Of 

 a pale grey colour, with bands of chocolate radiating from the apical 

 pole. Two specimens from the coast of Portugal, and fragments in 

 deep water oft' the south and west of Ireland. 



EcHINIDjii. 



Echinus, Link. 



1. E. melo. Lam. 



One or two small specimens off the coast of Portugal. 



2. E. Flemingii, Ball. 



The large typical form of this species was met with in deep water 

 off the Shetlands, but not abundantly. 



3. E. rarispina, G. O. Sars. 



4. E. elegans, D. & K. 



5. E. norvegicus, D. & K. 



The last three are critical species ; and although the extreme forms 

 are very dissimilar, in a large series there are so many intermediate 



