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



Myxilla rosacea, Lieberkiihn, sp., var. japonica, nov. (PI. XXVI. fig. 3; PI. XXVII. 

 figs. 8, 8rt, 8h, Sc ; PL XL VII. fig. 3). 



1859. Halichondria rosacea, Lieberkiihn, Arcliiv f. Anat. u. Physiol., vol. ix. p. 520, Taf. xi. 



fig. 2. 

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



1862. Myxilla fanciculata, Schmidt {non Lieberkiihn), ' Spong. AJriat. Meer., p. 71. 

 1864. Myxilla tridens, Schmidt, Spong. Adriat. Meer., Suppl. i. p. 30. 

 1864. Myxilla Esperii, Schmidt, Spong. Adriat. Itleer., Suppl. i. p. 36, 



Sponge (PL XXVI. fig. 3) lobate or digitate ; frequently flattened. The largest 

 specimen is of an irregularly lobate form and 56 mm. in length. Colour in spirit very 

 variable ; ranging from very pale, creamy yellow to almost quite black. Texture firm, 

 compact and rather leathery. Surface uneven, corrugated, and sometimes minutely 

 hispid. Dermal membrane very thin and transparent. Pores not very abundant, 

 scattered. Oscula few, small, scattered. 



Skeleton. — The main skeleton consists of a very compact and symmetrical reticulation ; 

 when seen in thin section (PL XLVII. fig. 3) the network appears to be made up of a 

 number of triangular meshes, the apices of six such triangles meeting in a common point 

 while the bases form a hexagon ; this arrangement is in places very distinctly visible but 

 is, of course, never mathematically exact. The sides of the triangular meshes are of 

 exactly one spicule's length, and are formed of from one to about six stylote spicules 

 lying side by side. There is no proper dermal reticulation, but at a depth of about 0'14 

 mm. below the dermal membrane the skeleton arrangement just described suddenly 

 gives place to another and totally difi"erent one. This takes the form of a number of 

 brushes of tornote spicules, each brush only one spicule in length, and with the com- 

 ponent spicules diverging upwards towards the dermal membrane, which they support, 

 and through which their points often project for a short distance. 



Sincules. — («) Megasclera; of two kinds, (l) Entirely spined, short, slightly curved 

 styli (PL XXVII. figs. 8, 8a.) tapering rather suddenly to a sharp point at the apex, size 

 about 0'14 by 0'0126 mm. (the diameter is very variable, that given is about the maxi- 

 mum), making up the main skeleton; (2) smooth, hastately pointed tornota (PL XXVII. 

 figs. 86. 8c) rather thicker in the centre than elsewhere, size about 0"175 by 0"007 mm., 

 occurring in brushes supporting the dermal membrane, {h) Microsclera ; of two kinds — 

 (1) small, tridentate isochelse, with rather strongly curved shaft, which appears to be 

 slightly expanded laterally, especially towards the two ends; length up to abowt 0'03 

 mm. ; (2) slender sigmata, usually much contort, length up to about 0"045 mm. 



This sponge difi"ers from Schmidt's types of the species chiefly in the possession of a 

 shorter, stouter, and more strongly spined stylote spicule ; in Schmidt's types, also, the 



1 According to Vosmaer, Notes Leyden Mus., vol. ii. p. 123, 1880. 



