382 HYALONEMA (SKIANEMA) AEQUATORIALE. 



very markedly. The distances between the ends of opposite teeth are therefore 

 smaller than the breadth of the anchor. While the latter is, as above stated, 

 90-195 M, the former is only 83-164 m, that is 7-20 ti less. The outer band- 

 shaped part of the tooth attains its maximum width of 17-29 m about two thirds 

 of its length from its base. Distally it is simply rounded off. The keel in the 

 larger forms is, at the base of the tooth, about 30 ix high, decreases in height 

 distally, and terminates some distance within the tip of the tooth. 



Besides the regular large macramphidiscs above described, a good many 

 irregular large macra?nphidiscs (Plate 99, figs. 18-20) have been observed. The 

 irregularity most frequently observed is an inequality of the two anchors of the 

 same spicule. These may differ in size, in the proportion of their length to their 

 breadth, and in the number of teeth composing them. The irregular large 

 macramphidiscs of this kind are about as large as the regular ones. Much more 

 rarely smaller forms are met, in which either a large conic protuberance arises 

 from the apex of one of the anchors (Plate 99, fig. 18) or the anchors are quite 

 irregular. The teeth composing such anchors are exceedingly unequal, some 

 being hypertrophied, twisted, or otherwise deformed, others rudimentary (Plate 

 99, figs. 19, 20). 



The small macram-phidiscs (Plate 100, figs. 1-4, 12; Plate 101, fig. 2c) are 

 70-120 n long, most frequently about 84.2 m- The shaft is straight, cylindrical, 

 perfectly smooth, and 6.5-13 m thick. The terminal anchors are 38-50 ix long, 

 about half the whole spicule, and 37-84 ^ broad. The proportion of the length 

 to the breadth of the anchors is 100 to 120-175, on an average 100 : 146.G. 

 Each anchor is composed of from ten to twelve teeth. The teeth of the two 

 anchors of the same spicule are generally situated alternately, but this alternation 

 is only exceptionally regular, usually it is more or less irregular. The individual 

 teeth are curved quite uniformly for the greater part of their length through 

 about a quarter of a circle, so that the whole anchor is more or less hemispherical 

 in shape. Their extreme tips are strongly bent inward and converge, so that 

 the distance between the ends of opposite teeth is usually about 6 n less than 

 the breadth of the anchor. The outer band-shaped part of the tooth attains its 

 maximum breadth of 10-14 n in its distal half, and is rounded or, more rarely, 

 blunt-pointed at the end. 



Differences in the number of teeth of the two anchors of the same spicule, 

 differences in the size of the teeth of the same anchor (Plate 100, fig. 3), and other 

 irregularities often occur. 



The large rnicramphidiscs (Plate 99, figs. 11-16) are 54-84 ^ long, most 



