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THE VOYAGE OE H.M.S. CHALLENGER. 
3. Protriaene, rhabdome 3 '2 by 0*018 mm. ; cladi 0*17 mm. long (Bwk.) ; rbabdome 
5*4 by 0*013 mm. ; cladi 0*15 mm. long, chord 0*084 mm. (Soil. C.). 
4. Anatrissne, rhabdome 2*1 by 0*011 mm. (Bwk.), rhabdome 3*9 by 0*012 mm. ; 
cladome subterminal, cladal centre 0*012 from the distal termination of the axis of the 
rhabdome cladi; 0’05 mm. long, chord 0*063 mm. (Soil. N.); rhabdome 11*4 by 0*02 mm.; 
cladome terminal, cladi 0*084 mm. long, chord 0*095 mm. (Soil. C.). 
II. Microsclere. 5. Sigmaspire, 0*0095 mm. long (Bwk.), 0*012 mm. long (Soil. N.), 
0*012 mm. long (Soil. C.). 
Habitat. — The Island of Arran ; Galway, Ireland (Bwk.) ; Shetland Isles, deep water 
(Bwk.); The Minch, deep water (Norman); Kors Fjord, Norway, 180 to 300 fathoms 
(Norman, Sollas) ; lat. 61° 0' N., long. 4° 49' E., 200 fathoms, bottom, ooze and clay, 
temperature 6°*6 C. ; and lat. 72° 53' N., long. 21° 51' E., 223 fathoms, bottom, clay, 
temperature 1°*5 C. (Hansen) ; near the last mentioned locality, in 140 to 165 fathoms 
(Vosmaer) ; deep sea, between Faeroe Isles and North of Scotland (Carter). 
Remarks. — The initials (Bwk.) indicate measurements taken from Bowerbank’s descrip- 
tions ; (Soli. N.) measurements by Sollas of specimens dredged by Norman; (Soil. C.) 
measurements by Sollas of specimens described by Carter. None of these sets of 
measurements are accordant, except in the case of the cortical oxeas and the sigmaspires. 
The discrepancy is probably due to the spicules measured having been obtained from sponges 
of different size, thus Carter’s are many times larger than Norman’s specimens. As to the 
size of the specimens from which Bowerbank obtained his spicules we have no knowledge ; 
it would be worth while to re-examine some of the three hundred specimens obtained 
by Bowerbank, with a view to determining the size of their spicules anew. Mr. Carter 
has kindly sent me mounted spicules of the specimen of Craniella cranium figured by 
Bowerbank as seated in Phakellia ventilahrum ; these are of the largest size given in the 
preceding measurements. The spicules of Tethya unca, Bowerbank, have the same size 
as the larger ones of the foregoing descriptions, and it would seem just possible that the 
fact of their being about twice as long as those of Tethya cranium, as given in Bowerbank’s 
published measurements, led him to distinguish between the supposed two species ; on 
the other hand, he expressly states that the distinction rests on the smaller size of the 
sigmaspire in Tethya unca, and as, after an examination of specimens in the British 
Museum, I do not find even this difference to exist, I see no alternative but to include 
Tethya unca as a synonym of Tethya cranium. 
Norman describes as Tethya cranium, var. acufera, specimens in which one-third of the 
rhabdus spicules are strongyloxeas. Craniella zetlandica, Craniella ahyssorum and 
Craniella infrequens he also regards as varieties of Craniella cranium. Vosmaer’s proposal 
to re-name this species appears superfluous. The fact that Muller’s sponge, which appears 
to have l^een Craniella cranium, was erroneously identified as Alcyonium cranium, in 
