394 HYALONEMA (THALLONEMA) GEMINATUM. 



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the shaft is particularly strongly bent, convex towards the spine. The tenninal 

 anchors are 72-100 ^ long, a fourth to a third of the whole spicule, and 175-200 ix 

 broad. The proportion of the length to the breadth of the anchors is 100 to 

 182-257, on an average 100 : 223. The anchor is composed of from ten to fifteen 

 teeth. The individual teeth are usually more strongly curved in their distal 

 than in their proximal part. The extreme tips of the teeth are, if not widened 

 to terminal discs {vide infra), generally abruptly bent inward and convergent. 

 A larger or a smaller number, most frequently about half, rarely all, of these 

 teeth bear from one to three branches. Generally one anchor of the spicule 

 is richer in branched teeth than the other. The branched teeth consist of a 

 stem similar to an ordinary unbranched anchor-tooth, from the outer convex 

 side of which from one to three branches arise. These branches are curved 

 conformly with the stem from which they arise, concave towards the shaft, 

 and usually end in oval flattened extensions, which appear as terminal discs. 

 The end of the stem or main tooth, from which these branch-teeth arise, often also 

 terminates with such an extension. The outer faces of the simple teeth and of 

 the end-parts or terminal discs of the stem and the branches of the branched 

 ones lie in a continuous surface ovoid in shape, which I take to be the inner 

 face of the limit or wall of the living unit — in my opinion a single cell — 

 within and by which the amphidisc is formed. As stated above, transitional 

 forms with only one or two branched anchor-teeth (Plate 105, fig. 14) connect 

 these geminate with the ordinary large macramphidiscs described below. 



The ordinary large macramphidiscs (Plate 104, figs. 6, 7) are 133-271 ix long, 

 most frequently about 198.5 and 204.2 m- The shaft is 15-26 m thick, generally 

 straight, cyhndrical, and smooth, sometimes slightly bent, and occasionally 

 provided with one stout blunt spine about 20 /.i long. When such a spine is 

 present the shaft is always bent as in the geminate macramphidiscs. The termi- 

 nal anchors are 48-105 m long, a third to two fifths of the whole spicule, and 115- 

 203 n broad. The proportion of the length to the breadth of the anchors is 

 100 to 169-274, on an average 100 : 225.5. The anchor is composed of from 

 eight to eleven teeth. The number of teeth in the two anchors of the same 

 spicule is not always the same. The teeth of the opposite anchors often, but 

 by no means always, alternate. The individual teeth arise nearly vertically 

 from the ends of the shaft, are straight or only slightly curved in their basal 

 part, but strongly curved in their distal part. The outer band-shaped portion 

 of the tooth attains, in the larger forms, a maximum breadth of 25-29 n. Its 

 distal end is rounded and abruptly bent inward so that the tips of the teeth 



