182 HYALONEMA (HYALONEMA) AGASSIZI. 



The gastral pinnies of the cone of form D (Plate 42, fig. 24) resemble those 

 of form A rather closely. They have a distal ray 98-113 ju long, on an average 

 106.7 M, and 6.5-8.5 m thick at the base. Its maximum transverse diameter, 

 together with the spines, is 25-38 fi. The lateral rays are 26-64 /^ ; the proximal 

 ray (of the hexactine forms) is 38-50 /i long. 



The gastral pinules of form E have a distal ray 69-103 m long, usually 83- 

 99 n, on an average 90.5 m, and 4.5-7 ix thick at the base. Its maximum thickness, 

 together with the spines, is 21-37 m- The lateral rays are 21-57 /^ long. In two 

 hexactine gastral pinules of this form measured, the proximal ray was 42 and 44 yu 

 long respectively. 



The gastral pinules of form F have a distal ray 100-153 n long, on an average 

 129 n, and 5-6 ^ thick at the base. Its maximum thickness, together with the 

 spines, is 25-40 jj.. The lateral rays are 50-62 /x long. 



Minute pentactines with spiny rays (Plate 42, figs. 9, 50) were found in small 

 numbers in the spicule-preparation of the gastral cone of form A, and the basal 

 part of forms A and B. These pentactines have straight, conic, blunt-pointed 

 rays, smooth at the base, but covered with conspicuous spines in their distal part. 

 Their apical ray in form A is 36-80 fi long, in form B 43-65 m, and is in both 

 3-6 n thick at the base. The lateral rays of the same spicule are equal. In 

 form A they are 40-50 ix long, in form B 25-42 n, and about as thick as the apical 

 ray. 



The hypodermal pentactines of form A (Plate 41, figs. 3-11 ; Plate 45, fig. 23) 

 have a fairly straight, conic, and Islunt apical (proximal) ray, which measures 

 0.3-1.5 mm. in length, and 18-90 ^ in thickness at the base. The lateral rays of 

 the same spicule are fairly equal or more or less unequal. Among the small 

 hypodermal pentactines forms with equal lateral rays predominate, but among 

 the large ones forms with unequal lateral rays are the more numerous. The 

 lateral rays are more or less oblique and enclose angles of 80°-88° with the apical 

 (proximal) ray. They are usually somewhat curved, conic, and rounded at the 

 end. The longest lateral ray is 0.25-1.3 mm. long. The ends of the lateral 

 rays (Plate 41, fig. 9) are, as in Hyalonema obtusum, usually irregular, and proba- 

 bly for the same reason (c/. p. 160). 



In the forms B, C, and D, in which the greater part of the dermal membrane 

 is lost, only few hypodermal pentactines were found. All those observed in 

 forms C and D were similar to those of form A. In form B spiny pentactines 

 of similar dimensions were found, in addition to the ordinary smooth ones of the 

 other forms. For the reasons given below (p. 183) I consider these spiny pentac- 

 tines as foreign spicules. 



