EEPORT ON THE TETRACTINELLIDA. 
71 
a series of vesicles ; no other Thenea approaches it in the abundance of this tissiiOj 
except Thenea ivyvillii. In Thenea schmidtii it is comparatively scanty, even the main 
canals being but sparingly provided with it. 
3. Flagellated Chamhers. — These are considerably larger in Thenea schmidtii, being 
on the average of about twice the diameter of those of Thenea muricata. 
4. Distribution. — Thenea muricata is a northern species, found in company with 
Craniella cranium, auctt, Thenea schmidtii is a more southern form, with which 
Praniella schmidtii, n. sp., is associated. 
There may be a slight difference in colour between the two species, Thenea schmidtii 
being nearly white, and Thenea muricata a very evident grey, but I lay no stress on this. 
With regard to the differences which exist between different specimens of Thenea 
schmidtii, they are chiefly differences of external form and size — some resembling Thenea 
grayi, and others being agaricfform — and in the dimensions of the plesiaster, though not 
in its relative abundance. The rays of the plesiaster in specimens from Station lY. (depth, 
600 fathoms ; bottom, blue mud) are almost twice the thickness of those from Station 73 
(depth, 1000 fathoms; bottom, Pteropod ooze); it is to be supposed that the difference 
in the size of the plesiaster, in different examples of what has every appearance of being 
the same species, is due to some difference in local conditions, but from so small a basis 
of observation, one cannot connect it with the difference observed to exist in the depth 
and character of the sea-bottom. 
It only remains to explain the adoption of “ schmidtii ” as the specific name of the 
sponge. I avoided the designation “ agariciformis” because Schmidt did not at first call 
his Floridan specimens by this name, but simply stated that they resemble Tisiphonia 
agariciformis, Thomson, and he refrains from describing them because Thomson had 
previously sent him examples and plates illustrative of this sponge. As the Florida 
specimens are probably of the species just described, and Thomson’s is the northern 
form Thenea muricata, it would lead to confusion to credit Schmidt with Thomson’s 
name; while all uncertainty is avoided by the adoption of a new one. 
Thenea fenestrata (0. Schmidt) (PI. VIII. figs. 1-8). 
Tisiphonia fenestrata, 0. Schmidt, Spong. Meerb. Mexico, p. 71, Taf. x. fig. 2. 
Sponge (PI. VIII. fig. 1) cushion-shaped with an oval margin; upper surface rounded, 
rising in the middle into a conical eminence, truncated by the oscule at the summit. 
An equatorial series of poriferous areas (six to seven in number), separated by intervals 
where the upper and lower surfaces pass insensibly into each other over a rounded edge. 
As a rule only one large incurrent canal originates in the cavity lying beneath each 
poriferous sieve. 
The oscule is protected by a dense conical fringe of projecting oxeas ; spicular fringes 
