374 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



the body. The lining membrane of the pit is smooth and finely 

 porous, in upper part of pit showing the usual trichodal protriaenes. 

 Apertures of pits in general round, sometimes becoming slit-like in 

 closing; those widest open measure 6 mm. in diameter. Fringes 

 as in type, but very often worn down. 



What distinguishes these specimens at a glance from the type is 

 the presence of more or less circular, depressed, shallow, spinous 

 areas (doubtless oscular) on the upper surface of the body. Of these 

 there are often three or four in a specimen, but I have counted as 

 many as five and as few as two or, in the smallest specimen, only one. 

 The diameter of the areas ranges in general from 10 to 20 mm., the 

 depth from 1 to 3 mm. Both the margin and general surface of the 

 area are typically thickly covered with spicules that project about 2 

 mm ; these have been more or less rubbed off in many areas. The cov- 

 ering spicules of the area catch and hold sand in some quantity. The 

 surface of an area shows either no apertures at all or a number of 

 quite small ones, a fraction of a millimeter in diameter. These are 

 doubtless oscula; where they appear to be absent, they no doubt are 

 simply closed. No other oscula occur in the sponge. The small 

 oscula of this variety evidently correspond to those described by 

 Kirkpatrick (1905) for Cinachyra barbata, although their distribu- 

 tion is different. If the inferences generally drawn from anatomy 

 are correct, it would seem that in this species we have two classes 

 of oscula, the small ones of this variety and the large ones of forma 

 aperta. One may hazard the guess that there are both afferent and 

 efferent poriferous pits, the detailed features of which vary with the 

 physiological state, and small oscula as well. 



The ectosomal anatomy is as in the type. The skeletal arrange- 

 ment is as in the type. As in the type, the specimens are commonly 

 infested with a small brown actinian. 



Spicules. — 1. The oxeas of radial bundles, ectosome, and choano- 

 some are as in the type. 



2. (a). The promonaenes of the radial bundles are as in the type; 

 rhabdome commonly about 28 [l thick; clad commonly 200-250 \l long. 

 The prodiaenes and protriaenes of the radial bundles do not differ 

 from those of the type. 



(b). Protriaenes and prodiaenes with short and comparatively 

 stout clads, 35-85 \i long, project from the radial bundles over the 

 general and basal surface as in the type. 



(c). Protriaenes of the fringes of the poriferous pits, thickly 

 crowded and resembling those of the type ; rhabdome 8-10 mm. long, 

 clads 70-150 n long. The prodiaene is commoner than the triaene 

 form. 



