134 THE VOYAGE OF H.M.S. CHALLENGER. 



about 0"04 mm. ; (2) simple and contort sigmata, measuring up to about 0"063 mm. in 

 length, but varying greatly in this respect. 



This species resembles HalicJiondria isocUctyalis of Carter,^ but the chelse, sigmata 

 and styli are all smaller in that species than here, and further, the head of the stylus is 

 smaller than the shaft. 



Locality. — Off the south-west coast of Patagonia (Station 308 or 311, or both). 

 Five specimens. 



Myxilla spongiosa, Ridley and Dendy (PL XXVII. figs. 3, 3«, Zh, 3c, '^d, 3e, 3f). 



1886. Myxilla spongiosa, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. p. 471. 



Sponge massive, encrusting, growing all round a worm-tube, which it encrusts for a 

 length of 69 mm. and to a thickness of about 12 mm. in the middle. Texture 

 extremely soft and spongy. (The condition of the sponge is so bad that no further 

 account of the external characters is practicable.) 



Skeleton. — (a) Dermal ; a thick but confused reticulation of scattered tylote spicules. 

 (6) Main ; a very confused reticulation of smooth styli. 



Spicides. — (a) Megasclera; of two kinds; (1) smooth, stout, slightly curved styli 

 (PI. XXVII. fig. 3), tapering gradually to a sharp point at the apex; size about 07 by 

 0"02 mm. ; making up the main skeleton. (2) Tylota (PI. XXVII. figs. 3a, Zh), with 

 well-developed oval heads, usually (? invariably) minutely spined at the end ; size up to 

 about 0"4 by O'Ol mm. ; dermal. (6) Microsclera ; of two kinds ; (1) tridentate isochelse 

 (PI. XXVII. figs. 3c, 3(i), with the shaft laterally expanded towards each end ; length 

 about 0"0.5 mm. (2) Rather stout sigmata (PI. XXVII. figs. 3e, 3/"), usually much 

 contort; size about 0'063 by 0'0045 mm. Both kinds of microsclera are abundant. 



The condition of this specimen unfortunately prevents more detailed description, but 

 the spiculation is suflicient to distinguish it from other species ; it will be seen to 

 approach Myxilla mollis, nobis, in this respect, but difi"ers in details, Besides having 

 the stylus smooth, as in Myxilla mollis, the species further diverges from the more 

 normal character of Myxilla in the large size of the megasclera ai^d chelae. 



Loca%.— Station 320, February 14, 1876 ; lat. 37° 17' S., long. 53° 52' V^. ; ofi"the 

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

 ture, 37°"2. One specimen. 



Myxilla hastata, Ridley and Dendy (PI. XXVII. figs. 1, la, lb, Ic). 



1886. Myxilla hastata, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii p. 472. 

 Sponge forming a flattened lamella, the shape of which cannot be ascertained, as 

 there are only fragments in the collection. The largest piece measures about 69 mm. by 



1 Ann. and Mag. Nat. Hist., ser. 5, vol. ix. p. 285. 



