Sponges from the Atlantic Ocean. 405 



perfect in deurcssions wlicre it lias been protected from contact 

 with external objects. 



From tlie variety and number of foreign objects imbedded 

 in the dermal sarcode, it would a])j)ear as if the frai^ments of 

 this sponge had been currcntcd about over the deep-sea bottom 

 while they were still growing, thus adding to their struc- 

 ture — or, in a fixed position, had grown in the midst of deej)- 

 sea detritus, thus with their horrible roughness closely resem- 

 bling the fragments of Pachastrella ahyssi with which they 

 are associated : they are very disagreeable to handle, and very 

 dangerous, from the coarseness of their spicules, to the object- 

 glasses of a microscope. 



Tethi/a cranium, var. ahijssorum. (PI. XVI. fig. 49.) 



With reference to this variety, which abounds among the 

 dredgings of the ' Porcupine,' chiefly from tlie deep sea sepa- 

 rating the north of Scotland from the Fiiroe Islands, I can 

 see so little difference between it and that of T. cranium of 

 more shallow water, viz. from the Haaf banks off Shetland, 

 that the special designation of this variety merely rests on 

 the larger size of the fiesh-spicules (bihaniates), which, under 

 ;^-inch compound power (= about 400 diameters), are seen to 

 be covered with minute vertical spines, while those of T. cra- 

 nium in the British Museum are only half the size and the 

 spines on the surface hardly visible. In the variety, the Hesh- 

 spiculcs are 4-6000ths inch long (PI. XVI. fig. 49). 



This seems to be equally prolific with the sj)ccimen of T. 

 cranium figured in the 'Annals' (1872, vol. ix. pi. 22. fig. 13) 

 to show its pregnancy with ova and embryos in various stages 

 of development ; for there is hardly a specimen among the 

 sponges dredged up by the ' Porcupine ' which has not one 

 or more in various degrees of development adhering to it. 

 (The same might be said, almost, of 7'^6•^y)/*o?^^rt agariciformis.) 

 In their natural state, all the specimens of T. cranium are 

 covered with the heads of the projecting anchoring-spicules ; 

 but while the forked forms frequently remain, the recurved or 

 anchor-headed ones have their arms for the most part broken 

 off. The bihamates, too, although scattered throughout the 

 sarcode, arc, as Dr. Bowerbank lias observed, most plentifully 

 congregated in the dermal layer. 



Tcthya cranium, var. infrequens. (PI. XVI. fig. 48.) 



Another variety of T. cranium was dredged up at station 

 57 in 632 fathoms ; but as there is only one specimen of it, 

 I am unable to state if it be a normal or a pathological develop- 



