THE SPONGES. 61 



oxyhexasters of F. 7nexicana exhibit toward those of F. occa, there seems 

 to be ail agreement between it and F. aculeata. 



The dermal clavulae are with few exceptions umbellate forms (Fig. 8, 

 Plate 7), having commonly 12 to 16 teeth in the umbel, occasionally 

 less than 12 or more than 16. The stalk including the enlarged upper end 

 is smooth except near the point, where it is roughened. The length of 

 the spicule is about 320 /a. 



On the dermal surface are found a very few of the anchor-like clavulae 

 which are common on the gastral surface. Both kinds of dermal clavulae 

 are in place, in the usual position round a pentact, the number actually 

 present in a group being small, 3-6. 



The gastral clavulae are in part umbellate, in part anchor-like forms. 

 The former, which perhaps are the more abundant, do not differ from the 

 type which is found on the dermal surface. The anchor-like forms occur 

 in the usual position with respect to the pentacts. Frequently such a 

 spicule is found alone, sometimes together with a few of the umbellate 

 spicules. Where the spicule is alone, it is of course probable that the other 

 members of the group have fallen out. In this spicule (Figs. 4, 5, 10, 11, 

 Plate 7), the stalk is about 500 ju, long, smooth, practically straight, or 

 slightly or strongly curved, becoming very slender and ending below in a 

 point. It terminates above in a rounded knob, below which there is no 

 conspicuous bulb-like swelling. The knob bears 4 or 5 curved strong 

 teeth, which in some spicules, but not in all, have a slight spiral curvature 

 (Fig. 11, Plate 7). A short distance below the head, the stalk bears 

 iisually two curved lateral spines, sometimes only one, and occasionally 

 none. The curvature of the spines themselves varies, sometimes being 

 simple, again feebly spiral, while rarely the spines are straight. While the 

 head ordinarily bears 4 or 5 teeth, spicules are occasionally observed with 

 but 3 teeth (Fig. 5, Plate 7). As regards length of the teeth and width 

 of the umbel (anchor), the anchor-shaped spicule varies considerably. 

 While always larger than the many-toothed umbellate spicule, it is some- 

 times only about twice as wide, and again fully four times as wide as the 

 latter, across the umbel. The actual length of the teeth varied, in the 

 numerous spicules measured, from 24 /a to 48 /x, and the width of the umbel 

 (anchor) from 32 ^ to 88 /a. 



In the obviously closely related species Farrea acxdeata F. E. Sch. 

 (Schulze, 1899, p. 70), the dermal and gastral clavulae are alike, and essen- 



