REPORT ON THE MONAXONIDA. 



217 



case, however, the object of the flattened form and the long radiating spicules is obvious, 

 namely, as pointed out by Sars, to support the animal in the soft mud on which it lies ; 

 in our new species, Trichostemma sarsii, this arrangement is brought to a much greater 

 degree of perfection than in the original type of the genus [vide PI. XLIII. figs. 1, 1«, 

 2, 2«, 3, 3a, and woodcut, Fig. 8). 



The genus has a very wide geographical range, being found in deep water off the 

 north of Scotland (Carter), ofi" the coast of Norway (Sars, Hansen), Gulf of St. Lawrence 

 (Whiteaves), off the Azores (Challenger), ofi" the north-east coast of Australia (Challenger), 

 off the west coast of South America (Challenger), and in the Arctic Sea (Vosmaer). 



The question as to whether Schmidt's genus Radiella is really the same as Tricho- 

 stemma is a very difficult one. His generic diagnosis is not very recognisable ; it runs as 

 follows: — " Suberiten mit radiarer Schichtung derNadeln; ohne Wurzeln und ohne wahre 

 Einde, d. h. ohne Einde mit Faserelementen. Oscula vorhanden."^ The type of his 

 genus, Radiella sol, is undoubtedly extremely like our Trichostemma sarsii, and the fact 

 of its being also found in deep water (Cuba, 638 fathoms) perhaps strengthens the 



Fig. 8. — Trichostemma sarsii. Vertical section, showing the arrangement of the skeleton ; /, fringe of long, projecting 

 spicules ; c, cortical layer of vertical spicules ; d, external layer of foreign objects, dirt, &c.; ch, choanosome, containing 

 stellate groups of spicules ; th, " thatch " of spicules on the lower surface of the sponge. x 5. 



probability of their being closely allied. According to Schmidt's figure- the external 

 form of the sponge is almost identical with that of Trichostemma sarsii, but judging by 

 his description and figure there is no superior cortical layer and no internal confused mass 

 of spicules, the smaller spicules instead running continuously from the lower to the upper 

 surface of the sponge, beyond which they project "uumerklich." The thatch-Hke coat 

 of radiating spicules on the lower surface of the sponge seems to be the same as in 

 Trichostemma sarsii. In form also the spicules of the two species seem to be about the 

 same, but Schmidt gives no measurements. 



On the other hand Hansen^ states that he has examined an original specimen of 

 Radiella sol and identifies it with Trichostemma hemisphwriciim. 



Considering, therefore, that the name Trichostemma was used by Sars so far back as 



1 Spong. Atlant. Gebiet., p. 48. 



3 Norwegian North-Atlantic Expedition ; Spongiadfe, p. 7. 



(ZOOL. CHALL. EXP. — PART LIX. — 1887.) 



2 Loc. cit, pi. iv. fig. 6. 



Nnn 28 



