128 THE VOYAGE OF H.M.S. CHALLENGEE. 



curved styli (PI. XIX. fig. 4), tapering very gradually to a sharp point at tlie apex and 

 evenly rounded at the base, size about I'O by 0'037 mm.: making up the main skeleton. 

 (2) Tylota (PI. XIX. fig. 4a), with smooth, straight shafts and oval heads, which are 

 usually more strongly developed at one end of the shaft than at the other ; indeed 

 they may be almost absent at one end ; the ends of these spicules are very slightly spined 

 and sometimes flattened^; size about 0"525 by O'Ol mm.; dermal, (b) Microsdera ; 

 small, palmate isochelse, thickly strewn through the dermal membrane and also abundant 

 in the tissues below ; length about 0"02 mm. We have also observed a few large, slender 

 toxa with very faintly spined ends, length up to about 0'2 mm., and a few, usually 

 contort sigmata, length about 0*063 mm. 



This is an interesting species, and it is a pity that there are not more and better 

 specimens of it. It unites the characters of most species of Amphilectus, viz., the posses- 

 sion of smooth stylote megasclera and of small palmate isochelae, with a feature 

 which is very characteristic of the genus Myxilla, viz., the possession of a tylote 

 dermal spicule. Possibly the new species may form an important connecting link in 

 this very perplexing series of sponges. 



Zoca%.— Station 320, February 14, 1876; lat. 37° 17' S., long. 53° 52' W.; ofi" 

 the mouth of the Rio de la Plata ; depth, 600 fathoms ; bottom, green sand ; bottom 

 temperature, 37°"2. 



Subfamily 2. Ectyonin^. 



1875. Edyonida, Carter, Ann. and Mag. Nat. Hist., ser. 4, yoL xvi., p. 133. 



1886. Edyoninx, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. p. 470. 



Skeleton fibre echinated by laterally projecting spicules. 



Genus MyxUla, Schmidt (Pis. XXVL, XXVIL, XXX., XLVIL). 



1862. Myxilla, Schmidt, Spong. Adriat. Meer., p. 71. 



1880. Hastatus, 2}. P; Vosmaer, Notes Leyden Mus., vol. ii. p. 136. 



Megasclera of at least two kinds : — (1) monactinal : — styli, usually spined, main 

 skeleton spicules ; (2) diactinal : — variously ended ; strongyla, oxystrongyla or tylota, 

 chiefly dermal ; to these are sometimes added (3) small spined styli, which echinate the 

 main skeleton. Usually there is only a very small amount of spongin present. Micro- 

 sdera tridentate isochelae, to which sigmata are often added. 



The genus Myxilla was founded by Schmidt in 1862 {loc. cit.), and the first species 

 which he places therein is Myxilla rosacea, Liebkhn. sp. The original diagnosis runs 

 as follows : — " Halichondriae polymorphse, moUes et mucosae, fragiles, fere omnes spiculis 

 nodosis insignes," to which the author adds, " Ich gebe gern zu, dass diese Gattung auf 



1 It is doubtful whether flattening ever takes place at the larger end of the spicule. 



