HYALONEMA (HYALONEMA) AGASSIZI. 179 



Peculiar, very variable, modified pinnies (Plate 42, figs. 38-41, 43-45, 47, 

 48) occur in the basal region, where the large stalk-spicules enter the sponge- 

 body. These spicules appear to be dermal pinules changed in shape and in part 

 pushed into the interior by the stresses arising in this region from the resistance 

 of the embedded upper ends of the stalk-spicules to the weight of the sponge-body, 

 and to such passive movements of it as may be caused by the impact of moving 

 deep-sea animals. Transitional forms appear to connect these modified pinules 

 with the slender-rayed, long-spined basal tetractines and other spicules described 

 below. 



The modified basal pinules of form A (Plate 42, figs. 38-41) are pentactine 

 or hexactine. The distal ray is straight, 78-120 n long, and 2.5-6 fi thick at the 

 base. It bears, in its middle- and end-parts, sparse, strongly divergent spines, 

 which are sometimes irregularly distributed, and are more numerous on one side 

 than on the other (Plate 42, fig. 40). These spines are slender, conic, pointed, 

 straight or slightly curved, simply or in an S-shaped manner; they are 15-29 n 

 long and 1.3-3 n thick at the base. The maximum transverse diameter of the 

 distal ray, together with the spines, is 18-42 ii. The lateral rays of the same 

 spicule are equal or unequal. They are straight, 30-57 n long, conic, usually 

 pointed, and covered with spines directed obliquely outward. The largest 

 of these spines are 1.5-2 /i long. The proximal ray (of the hexactine forms) 

 is 42-55 M long; in shape and spinulation it resembles the lateral rays. 



The modified basal pinules of form B (Plate 42, figs. 47, 48) are similar but 

 have shorter and stouter rays. The distal ray is 83-94 ai long and 4-6 m thick 

 at the base. Its maximum diameter, together with the spines, is 28-35 /i. 

 The spines of the distal ray are 18-24 /x long and 2.5-2.7 m thick at the base. 

 The lateral rays are 25-32 fj. long. 



Some of the modified basal pinules of form C (Plate 42, figs. 43, 44) are 

 considerably larger than those of the other forms. The distal ray is 101-135 ^ 

 long and 4.5-5 m thick at the base. Its maximum transverse diameter, together 

 with the spines, is 13-33 fx. Its spines are 14-15 yu long and about 2.3 n tliick 

 at the base. The lateral rays are 20-80 fi long. 



In form D, E, and F, I found only few modified l)asal pinules (Plate 42, fig. 

 45). One of form D which I measured had a distal ray 82 ^ in length and, 

 together with the spines, 28 n in maximum thickness. Its largest spines meas- 

 ured 18 by 2.5 M. 



The frill on the margin of the gastral wall, containing the diadine -pinules, 

 is preserved in a satisfactory manner only in the specimen of form A. The 

 diactine marginal pinules of this form (Plate 44, figs. 1-5) have a total length 



