BATHYDORUS LAEVIS SPINOSISSIMUS. 95 



men (C) is 39 mm. high and of varying breadth, 7 mm. below, 45 mm. above. 

 This specimen has a slender protuberance 11 mm. long and 2.5 mm. thick, 

 which arises from the outer (lower) convex side of the broad rounded bottom of 

 the calyx. Another calyculate specimen is more slender, 28 mm. high, 8 mm. 

 broad below increasing to 25 mm. above. The lamellar fragments measure 

 25-56 mm. in maximum diameter. 



Pores, mostly 200-400 m in diameter, on both sides of the calyx-walls 

 are observed. These are now open. In the living sponge they were probably 

 covered by (dermal and gastral) sieves. From the inner and the outer surface 

 large and small prostal spicules protrude. Most of these, particularly the larger 

 ones, are very slanting and enclose small angles with the surface. Pores are 

 observed also on the surface of the fragmentary lamellae, but these no doubt in 

 consequence of post mortem shrinkage and maceration are much wider than in 

 the better preserved calyculate specimens and have a maximum diameter of 

 1.5 mm. These fragmentary, lamellar specimens show but little of the protrud- 

 ing prostal spicules. 



The colour in spirit is light dirty brown with a greenish tinge. 



General structure. The superficial pores above referred to lead into canals, 

 in specimen A 300-400 n wide, which traverse nearly the entire thickness of the 

 lamella in a somewhat obUque direction (Plate 14, figs. 14, 15). Indications of 

 flagellate chambers can be made out in parts of the sections of this specimen. 

 It seems that they are small, spherical or shghtly oval, and 70-120 n in diameter. 



The skeleton of the interior consists chiefly of rhabds and oxyhexasters. 

 The former are exceedingly variable in size and extend paratangentially and 

 obliquely. The proximal parts of the prostals, which are imbedded in the 

 choanosome, also take part in the formation of its skeleton. Beneath the dermal 

 and the gastral membranes paratangentially situated rhabds form loose reticula- 

 tions. Fairly numerous hypodermal pentactines with rather long lateral rays 

 arranged in the usual manner are observed below the dermal membrane. Hypo- 

 gastral pentactines appear to be absent. The dermal membrane is occupied 

 by dense masses of spicules, the rays of which are on an average about twice as 

 long as the distance between their centres. These spicules are mostly regular 

 tetractine stauractines, but similar spicules with one or two shortened or entirely 

 suppressed rays (irregular stauractines, triactines, and diactines) occur. Similar 

 spicules with five or six rays (pentactines and hexactines) also occur in the dermal 

 membrane. The gastral membrane is occupied by more slender-rayed pinule- 

 like hexactines, generally with one more or less differentiated, outwardly directed 



