THE SPONGES. 31 



ray is commonly 150-200 fx long, with a basal thickness of 5 /x ; tangential 

 rays 30-40 />t long. Spicules in which the distal ray is only 100 /u, long, 

 or as long as 220 /x, occur. Tiie pinnies are abundant, and their tangential 

 rays rest upon the reticulum formed by the hypodermal diacts and the 

 tangential rays of the hypodermal pentacts. 



The gastral pinnies are in general like the dermal pinules ; but long, 

 very slender forms of the type shown in Fig. 2, Plate 1, occur. In these 

 spicules the spines on the distal ray are so reduced in size as to be mere 

 prickles. The distal ray is 300-400 /a long ; tangential rays about 40 /x 

 long. Transitional forms between these and the ordinary type of pinulus 

 occur. The gastral pinules are arranged in the same way as the dermal. 



Canalar pinules are rather sparsely scattered over the walls of the 

 larger efferent canals. They are similar to the common type of dermal 

 and gastral pinulus, but are somewhat shorter. The distal ray is 110-150 /a 

 long ; tangential rays 40 /x long. Only a comparatively small percentage 

 of the spicules rest upon the underlying diacts. 



The marginal ridge is well preserved in only one specim.en, that from 

 Station 3376. Oxydiacts (marginalia) in considerable number project 

 radially from the ridge. Many are like the common hypodermal diact ; 

 i. e., smooth and enlarged at tlie middle. Others are specialized marginalia, 

 in which the outer projecting half is covered with small, sharp spines, while 

 the inner half is smooth (Fig. 1, Plate 1). An occasional prickle is found 

 in some spicules on the inner half. A typical spicule is 700 /x long and 

 12 /x thick near the middle. This form of marginal diact is shorter and 

 slenderer than the common sizes of the smooth form. 



The characteristic macramphidisc of the species is shown in Figs. 5, 

 6, and 7, Plate 1. The shaft is ordinarily smooth, very rarely with one or 

 two rounded protuberances at the middle. The umbels have the thape 

 of wide shallow bowls ; depth of the umbel about -| total length of the 

 spicule, or less ; umbel rays 8 in number, broad and leaf-like, pointed. 

 In the specimens from Stations 3376 and 3363 the macramphidiscs are 

 alike. In these specimens the total length of the spicule is 100-200 /x; 

 thickness of the shaft at the middle 8-16 /x ; depth of the umbel varying 

 somewhat, but close to I the total length. One of the smaller sizes is 



shown in Fig. 5, one of the larger in Fig. 6. In the specimens from 



Station 17 (1900 cruise), macramphidiscs occur that are similar to those 

 of the other specimens, but in most of the spicules the umbels are very 



