1872.] 



1 Porcupine ' Dredging -Expeditions. 



493 



It occurs abundantly in the Mediterranean, and locally off the coast of 

 Portugal. 



Porocidaris, Desor. 



This genus was established by Desor chiefly on a character which I cannot 

 regard as of great importance, and which is absent in the present species, a 

 row of small holes surrounding the tubercles of the primary spines in the 

 scrobicular areae. From the description these holes seem to be nothing 

 more than complete perforations, owing to imperfect calcification, in the 

 position of the depressions which frequently occur in the scrobiculse of the 

 Cidaridse for the insertion of the muscles of the spines. Along with this cha- 

 racter, however, there were some others of greater value, a very remarkable 

 paddle-like form of the spines surrounding the mouth, and a tendency to 

 coalescence in the scrobicular areae. These characters are well marked in 

 the species described. This genus has hitherto only been found fossil — 

 a few detached plates and some of the characteristic spines in the Num- 

 mulitic bedsof Verona and Biarritz, and some spines referred to the genus, on 

 account of their having the same singular form, in the Lower Oolite of Frick. 



1. P. purpurata, n. sp. 



Four examples from depths from 500 to 600 fathoms off the Butt of the 

 Lews. 



ECHINOTHURIDJS. 



I think it due to the memory of the late Dr. S. P. Woodward to adopt 

 as the type of this very distinct and remarkable family the genus Echino- 

 thuria, which he described with singular sagacity from one or two imperfect 

 specimens from the White Chalk. The EchinothuridDe are regular urchins 

 with depressed tests, rendered perfectly flexible by the whole of the 

 plates, both ambulacral and interambulacral, being arranged in imbricating 

 rows, the interambulacral plates overlapping one another from the apex to 

 the mouth, and the ambulacral plates in the opposite direction. The margin 

 of the peristome is entire, and the peristomial membrane is covered with 

 imbricated 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 intercalated 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. 



