THE PORIFERA. 93 



approximated, on the same plane, more or less covered by 

 small sagittiform triradiates. Pores situated in the inter- 

 stices between the arms of the triradiates, along the intervals 

 of the large acerates. Vent single, at the end of each branch, 

 naked, i.e., without peristome ; leading into a cylindrical, 

 cloacal cavity, about the same shape as the sponge, and 

 equally branched ; presenting on its surface a great number 

 of circular holes in juxtaposition, rendered more or less 

 polygonal by the intercrossing of the rays of the radiates 

 that form the skeletal structure of the cloaca, which is 

 sparsely echinated by the fourth ray of the quadriradiates. 

 Wall consisting of simple, cancellated sarcode, traversed 

 horizontally, at intervals, by the shafts of large, sagittiform 

 triradiates which, coming from opposite sides and over- 

 lapping each other, have their heads in the internal surface 

 of the cortex and that of the cloaca respectively. 



Spicules of three kinds, viz., acerate, triradiate, and 

 quadriradiate. 1st, acerate, very large, long, fusiform, slightly 

 curved, and often lance-pointed anteriorly, averaging ^th inch 

 long by 2 lyth inch in its greatest transverse diameter ; 

 2nd, triradiates, small and large, the latter averaging t^ho by 

 Y^'ooth inch in the shaft, and the arms respectively frds of 

 this size ; 3rd, quadriradiates, of the same size as the large 

 triradiates, with the addition of the fourth arm which is short 

 and curved, about y^^ooths inch long. No. 1 is confined to 

 the surface with the arrangement before stated ; No. 2 in its 

 larger form, to the wall, also as above stated ; and the 

 smallest, which are chiefly sagittiform, to the outer and 

 inner surfaces ; No. 3 to the inner part of the cloaca, where 

 they are formed by the addition of the fourth arm to the 

 heads of the large triradiates of the wall which abut against 

 this part ; thence projecting into the cavity of the cloaca^ 

 Size of specimen, which is much broken, under yVth inch 

 in the diameter of the stem ; length unknown ; longest 



