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 /x long, on an average 
106.7 yu, and 6. 5-8. 5 n thick at the base. Its maximum transverse diameter, 
together with the spines, is 25-38 /z. The lateral rays are 26-64 /x; the proximal 
ray (of the hexactine forms) is 38-50 m long. 
The gastral pinnies of form E have a distal ray 69-103 /x long, usually 83- 
99 /x, on an average 90.5 and 4.5-7 /x thick at the base. Its maximum thickness, 
together with the spines, is 21-37 m- The lateral rays are 21-57 m long. In two 
hexactine gastral pinules of this form measured, the proximal ray was 42 and 44 /x 
long respectively. 
The gastral pinules of form F have a distal ray 100-153 /x long, on an average 
129 fji, and 5-6 m thick at the base. Its maximum thickness, together with the 
spines, is 25-40 n. 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 m long, in form B 43-65 n, and is in both 
3-6 m thick at the base. The lateral rays of the same spicule are equal. In 
form A they are 40-50 /x long, in form B 25-42 yu, 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 blunt apical (proximal) ray, which measures 
0.3-1. 5 mm. in length, and 18-90 /z 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. 
