REPORT ON THE TETRACTINELLIDA. 
99 
mination of a specimen sent me by Mr. Whiteaves, along with, other sponges which he 
obtained there. After a critical comparison of this with Bowerbank’s types, I can dis- 
tinguish no difference of specific value. The spicules agree remarkably well in dimen- 
sions, the only difference in this respect being the presence in the American specimen of 
some very slender forms of oxea, 2'5 by 0 '01 6 mm. in length aud breadth, which are 
absent in the British forms. The occurrence of the same species in such widely separated 
localities is explicable on the supposition that its distribution is Arctic — an idea which is 
supported by the fact that it has not been dredged south of latitude 57° N., other species 
replacing it as we proceed southwards. It probably belongs to the northern group in 
which Thenea muricata and Craniella cranium are included. 
Pcecillastra scahra (O. Schmidt). 
Stelletta seabra, O. Sch., Spong. Adriat. Meeres, Suppl., iii. p. 19, pi. iv. fig. 3, 1868. 
Sponge. — A flat cake-like mass, about 20 mm. thick, and as large as a hand ; ecto- 
some but slightly developed ; canals large and open. 
Spicules. — I. Megascleres. 1. Oxea, fusiform, 0'887 mm. long. 2. Orthotrisene, 
rhabdome 0T775 mm., cladi 0’05 mm. long. 
II. Microscleres. 3. Microxea, with an irregular nodose or roughened surface, 0T27 
mm. long. 4. Spiraster, 0‘0316 mm. long. 
Habitat. — Coast of Algiers. 
Remarks. — The dimensions of the spicules were obtained by measurements made 
from a type-slide in the British Museum collection. I did not succeed in finding' any 
true asters, and as the general facies of the spicules is more that of Pcecillastra than 
Stelletta, I with some hesitation refer the sponge to the former genus ; it may possibly 
be more nearly allied to Characella. The megascleral oxea is remarkably small, and if 
the spicules on Schmidt’s slide fairly represent those of the sponge, it may be considered 
as affording a good specific character. 
Pcecillastra amygdaloides (Carter). 
Pacliastrella amygdaloides. Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xviii. p. 406, pi. xiv. 
fig. 22, 1876. 
Sponge. — A rounded mass, sessile ; surface even, rough ; oscule, the patent opening 
of a shallow cloaca ; pores in the interstices among the microxeas. Size, 25 mm. long 
by 15 mm. broad and 10 '5 mm. high. 
Spicules . — I. Megascleres. 1. Oxea, fusiform, sharply pointed, 1‘62 by 0‘014 mm. 
2. Triod, actines 0'7 by 0’06 mm. The rudiment of a fourth actine is represented by 
a short axial fibre, and is sometimes developed into a short strongylate cylindrical 
process. 
