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 
25-50 mm. in maximum diameter. 
Pores, mostly 200-400 /i 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 a wide, which traverse nearly the entire thickness of the 
lamella in a somewhat oblique 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 slightly oval, and 70-120 ^ 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 
