102 Mr. H. J. Carter on a neio Species of Tethya. 



and contractile sarcode, which, after death, from its stringent 

 contractility, renders the branching of the excretory canal- 

 system almost imperceptible. 



In addition to the form, then, of the entire sponge, we have 

 the absence of the anchor-head and the presence of the minute 

 unequal-armed trifid spicule of the sarcode as the peculiarities 

 of T. casula. 



The absence of sarcode also in the summit of the conical 

 expansion of T. casula renders it very doubtful if there ever 

 were any pores and vents in this part of the cavity, especially 

 as, in situ^ the whole of the cavity must have been shut out 

 from the sea by insertion in the sand of the greater part, at 

 least, if not the whole, of the conical expansion, in no part of 

 which are there any polygonal interstices or other indications 

 of pores and vents such as are seen on the surface of the head 

 or body. 



Of the colour it can only be stated,' as above, that in the 

 dried state it is light greyish yellow, exactly like that of T. 

 arahica in a similar condition, but which, when fresh, presents 

 internally an orange-yellow sarcode with pinkish nucleus ; 

 while Tethya dactyloidea^ Cart., and T. atropurjjurea, C, are 

 both dark purple on the surface and, for the most part, 

 throughout. 



Of the habitat of T. casula we know nothing further than 

 may be learnt from the specimen, viz. that it did not grow in 

 a pendent position, but in the sand at the bottom of the sea, 

 as the presence of the sand testifies ; that is to say, we do not 

 know whether it lived in deep or shallow water. The speci- 

 men of T. arahica^ which I found in situ on the south-east 

 coast of Arabia, was growing on the basaltic rocks of the 

 shore, where, having been left uncovered by the tide at low 

 water, I found it ; and so resistant was it, that I had to dig it 

 oiF in pieces with hammer and chisel. All that is stated of 

 T. cranium is that it adhered "to stones in deep water" 

 (Johnston, Brit. Spong. p. 83). Schmidt (Atlant. Spong. 

 Faun. p. 66) also mentions that T. cranium was found off 

 Florida in 152-183 fathoms ; but nothing is stated in this 

 respect of his Tetilla euplocamus or T. polyura. 



Undoubtedly the office of the conical expansion in T. casula^ 

 of the twisted cord in Tetilla euplocamus, Sdt., of the beard- 

 like tufts in T. polyura^ Sdt., and of the beard of Tetliya dac- 

 tyloidea, Cart., is the same as that of the stem in Hyalonema^ 

 already noticed by Schmidt ; but while the longest spicules in 

 the Tethyadae do not exceed half an inch, those of Hyalonema 

 are more than half a yard. Still, when it is stated that the 

 anchor-headed spicules are for the purpose of fixing the Te- 



