98 OPHIOPHOLIS BELLIS. 



green arms, banded with lake-red ; &c. The very young animals cling to 

 the arms of their parents, sometimes one on top of the other. A young 

 one, with a disk of 1.7"""', had arms 4.4°'"' in length ; the disk had only a 

 few scattered, small, trifid spines round the margin ; in the centre was a 

 rosette of primary 23hites, which still preserved their form ; these were 

 surrounded by twenty-five more plates, viz., a primary plate and two 

 radial shields in each brachial space, and two primary plates in each 

 interbrachial ; all the plates were very thin, and composed of a network 

 of fine spicula3 ; the upper arm-plates were longer than broad, broadest 

 in front, and rounded throughout ; in place of supplementary pieces 

 there were two or three little thorny grains ; below, the lower arm- 

 plates were longer than broad, with outer and lateral sides nearly 

 straight, and at the inner end an angle ; the mouth-shields and side 

 mouth-shields were much as in the adult ; the teeth very few in num- 

 ber ; the arm-spines four, very thorny, the lowest one on the outer 

 joints armed w^ith hooks. As the animal grows old, the primary plates 

 become more numerous and more widely separated ; the sjoines of the 

 disk grow smooth and granular, and increase in numbers ; then they 

 elongate, and finally become so developed as to obliterate some of the 

 primary plates ; the arm-spines, from being slender and conical, become 

 stout and flattened, and the teeth increase greatly in number. Dr. 

 Liitken gives the following table, to show the relative increase of jDarts. 



Diam. ofDisk. Length of Arm. No. of Joints. Joints with Hooks. „f'^'"'%^^;J*"^."' 



" Circle of Grains. 



2mm. _ _ (^mm. _ 9Q 15 ..... 12 



3 40 27 



4 45-50 ... 33 20 



6 .... 33 63 



10 .... 60 86 



14 .... 72 .... 105 40-50 ... 18 



According to this, both the disk and the arms continue to grow, but 

 the latter the fiister. During the growth of the arms new joints are 

 formed, and this increase of joints seems greatest in the very young 

 animal. The new joints appear at the tip of the arm, and not at the 

 base, next the mouth. In moderate sized specimens the arms are 

 usually not more than four or five times longer than the diameter of 

 the disk. 



O. hellls is distinguished from O. Caryl and 0. Kennerlyl by greater 

 size and different number of naked primary plates. On the Grand 

 Manan it is abundant, at low-water-mark of the spring tides, among 

 sea-weed (A. E. Yerrill). In Boston Harbor the young are often found 

 on bits of floating sea-weed (Dr. Wheatland). On the Scandinavian 

 coasts it has been dredged in from three to sixty fathoms (Ilollboll, 



