SPONGES. 103 



Taprobane herdmani, n. sp. Plate I., fig. 8 ; Plate [V., fig. 2. 



Specimen (Plate L, tig. 8) consisting of a stout, erect plate or lamella, strongly 

 curved (almost into the shape of a cup). Surfaces more or less uneven, especially on 

 the outside (which bears numerous galls due to parasitic barnacles). The upper edge 

 is broadly rounded, and the base of attachment is slightly expanded, like the foot of 

 a cup. Both surfaces are slightly and unevenly hispid, the hispidation being almost 

 confined to the more depressed portions. Both surfaces are thickly studded with 

 minute, pustule-like, circular areas, hardly visible to the naked eye. These areas are 

 only about 0"3 millim. in diameter, and each hears the single aperture of an incurrenl 

 or excurrent canal surrounded by a well-developed sphincter membrane. The colour 

 (in spirit) is dirty grey : the texture compact and stony. Greatest height about 

 70 millims. ; thickness of lamella about 15 millims. 



The main skeleton is a very dense and compact reticulation of desmas, together 

 with loose wisps or brushes of long, slender oxea running at light angles to the 

 surface, beyond which their ends project so as to give rise to the hispidation. The 

 oxea seem to disappear more or less completely from the deeper parts of the sponge, 

 while around the apertures of the canal svstem, at any rate on the outer surface, 

 they may project as a scanty fringe. 



Spicules. (1.) Desmas (Plate IV., fig. 2); monocrepid and rather sparingly 

 branched, the branches usually coming off almost exclusively from one side of the 

 main axis, which is usually more or less strongly curved. Main axis and branches 

 more or less abundantly ornamented with rounded tubercles ; branches (? always 

 terminating in conical papilla?, which may be bifid at the apex. The union of these 

 desmas is so close and compact that it seems almost impossible to isolate an adult 

 spicule for measurement : but the total length, measured in a straight line from point 

 to point, appears to be about 0"36 millim. The thickness of the main axis, exclusive 

 of tubercles, is about 0"028 millim. 



(2.) Oxea; very long and slender, gradually and sharply pointed at each end; 

 commonly more or less curved or crooked; size variable; they are usually broken, 

 but two complete spicules measured about TO millim. by 0"008 millim. and l - 88 millim. 

 by 0*008 millim. respectively. 



(3.) Sigmata ; slender, contort ; total length in a straight line from bend to bend, 

 about 01 millim. : abundant throughout the sponge. 



One of the most characteristic features of this species is the arrangement of the 

 apertures of the canal system. These appear to be identical in form and arrangement 

 on the two sides of the sponge, but we may conclude from the analogy of other plate- 

 like and cup-shaped sponges that the apertures on the outer side are inhalant pores, 

 and those on the inner side vents. Each aperture, whether pore or vent, lies in the 

 middle of a circular area, sharply defined by the sudden cessation of the reticulation 

 of desmas at its margin. This area is occupied by a very well developed, iris-like 

 diaphragm, with abundant circularly and perhaps also radially arranged myocytes, 



