494 Prof. Wyville Thomson on the Echinidea of the [June 20, 



] . P. placenta, n. sp. 



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

 ments from deep water in the Rockall Channel. 



Calveria, n. g. 



Plates overlapping greatly in the middle line of the ambulacral and in- 

 terambulacral areee. Plates narrow, and leaving fenestras between them 

 which are filled up with membrane. Character of the peristome with re- 

 gard to the distribution of spines, the structure of the pore-arese, &c. nearly 

 uniform from the apex to the edge of the peristome. 



1. C. hystrix, n. sp. 



Fenestree 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 fenestrae 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 off the 

 south and west of Ireland. 



ECHJNIDJS. 



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 links, that 

 it is difficult to tell where the one begins and the other ends. It is 

 possible that they ought to be regarded as varieties, and lumped together 

 under Lamarck's name, E. acutus. 



6. E. microstoma, n. sp. 



Although I have great hesitation at present in proposing an addition to 

 the genus Echinus, I feel compelled in the meantime to separate this very 

 distinct form with a thin depressed test, a remarkably large periproct, 

 and a small peristome with the edge markedly curved inwards and a 

 uniform vivid red colour. E. microstoma is very abundant from 150 to 

 400 fathoms off the west coasts of Scotland and Ireland. 



Sjphcerechinus, Desor. 



1. S. esculentus, L., sp. 

 A marked variety, with a tall narrow test and white spines, in deep water. 



