REPORT ON THE TETRACTINELLIDA. 
295 
The resemblance of the different species of Discodermia to one another is in all cases 
very marked ; the present species appears to be distinguished by its usually smooth 
desma, and by the characteristic forms of its phyllotrisene, as well as by the general form 
of the whole sponge. It is very similar to Discodermia calyx, Doderlein, and may very 
possibly be identical with it. Doderlein represents some spined styles as occurring 
in Discodermia calyx, but it seems to me more than probable that these do not properly 
belong to the sponge, but to some incrusting Monaxonid. From Discodermia ornata 
it is distinguished by the character of its desma, and from Discodermia panoylia by this 
character and the form of its phyllotrisene, such forms as those represented in figs. 7-9, 
for instance, not being present in the latter sponge. 
As Doderlein has already pointed out, the claims to generic distinction of Racodis- 
cula, Zittel, so far as they are founded on the form of the phyllotrisenes, fail through 
the association of both Racodiscula and Discodermia forms in the same sponge ; the 
same remark will probably be found to apply to Zittel’s fossil genus Rhagadinia,^ the 
discotrisenes which he regards as distinctive being similar to those of Discodermia 
panoplia. On the other hand, it does not follow that Racodiscula is not a good genus, 
and with an amended definition it will be found adopted on a subsequent page. 
Discodermia panoplia, n. sp. (PI. XXXII. figs. 12-25). 
Sponge (PI. XXXII. fig. 12). — A small mass, with a broad, incrusting base, straight 
even sides ascending to an expanded summit, with well-rounded margin. Oscules 
several, small, occupying the summit of small conical elevations, situated in the upper 
surface of the sponge. Pores simple, singly distributed on the sides of the sponge. 
Spicules. — I. Megascleres. 1. Desma {^\. XXXII. fig. 13), of fairly regular tetrad 
form, with short, stout, cylindrical, simple or branched epactines, studded all over with 
tubercles (PL XXXII. fig. 14), which are either simply conical with rounded summits, or 
cylindrical, either with flat summits and rounded edges, or with expanded heads and 
secondary tubercles ; zygosis takes place chiefly at the ends of the epactines or cladi, 
which are highly tubercular; the length of the epactine is usually about 0T6 to 0’24 
mm., its thickness from 0'09 to 0‘1 mm. Three of the actines of the axial rod usually 
differ in length from the fourth, which is longer ; the three shorter are from 0’04 to 
0’45 mm., the fourth and longer is from 0'8'4 to 0‘9 mm. long. 
2. Discotrisene (PL XXXII. figs. 15-19), a short conical rhabdome with rounded or 
pointed end, expanding distally into a more or less circular or cymbal-shaped cladome, 
with entire, sinuate, or lobate margins. The axial rod extends the whole length of 
the rhabdome, but its cladal processes do not proceed further than 0’019 to 0‘026 mm. 
into the cladome. Rhabdome 0‘045 to OTO by 0‘02 mm.; cladome about OT mm. in 
^ Of. Zittel, loc. cit., pp. 87, 88. 
