NORTHUMBERLAND AND DURHAM. 145 



Genus. THYONIDIUM, (Dtiben and Koren.) 



Thyonidium hyalinum, Forbes. Glassy Sea-cucmnber. PL I., 



figs. 24-33. 

 Gucumaria hyalina, Forbes. Hist. Brit. Starfishes (1841), 



p. 221. 

 Thyonidium pellucidum, Diiben and Koren. Skand. 



Echin., p. 303. PL IV., figs. 15-17; and PL XI., 



fig. 57 but not Holothuria pellucida of Vabl). 



Rare, Northumberland coast, G. H. 



A single specimen of this rare species was taken on the North- 

 umberland coast during the dredging expedition of 1864, the 

 only one that has occurred, so far as I am aware. The spicules 

 are of an irregular form, sometimes approaching to an uneven 

 rounded shape, the perforations being either round or four to 

 six sided, the body spicules having a central elevated part, caus- 

 ing it to present the appearance of a sort of three-legged stool. 

 Largest spicules about i-trW of an inch in diameter, the perfora- 

 tions barely exceeding 10 go u of an inch across. 



Thyonidium commune, Forbes and Goodsir. Common Sea-cu- 

 cumber (of Forbes). PL II., figs. 1-18. 



Cucumaria communis, Forbes. Hist. Brit. Starfishes 

 (1841), p. 217. 



The dental apparatus only from deep water, J. A. 



A single specimen is said to have been dredged on the Dogger 

 Bank during the expedition of 1862. Unfortunately the speci- 

 men has been mislaid, and, never having seen it, I cannot per- 

 sonally attest to the occurrence of this species on our coast, not 

 having myself taken it. I am indebted to the Rev. A. M. Nor- 

 man for a mounted slide from which the figures of plate II., 

 numbers 1-18, have been drawn ; 1-5 representing the ordinary 

 body spicules, which, when mature, are about ttsVo of an inch 

 across, the largest of the perforations being only rwoo of an 

 inch. Figs. 6-17 represent the spicules from the suckers : these 



