BIHANG TILL K. SV. VET.-AKAD. HANDL. BA^B 18. AFD. IT. XIO 1. 71 



30^ to 40°, the 2 and o larger tban tlie 1 and 4, tlie absence 

 of any lacune on tlie upper alveolar side; the same broadly 

 curvate form of the external side of the pyramid ; the broadly 

 lunate symphysis; the epiphysis not much reduced; and the 

 sequence of the tive compressed but very nearly uniform in- 

 terradia uninterrupted. But the lamellate texture of the wings 

 is fully developed. 



Another group is bere represented by the genera Echin- 

 arachnius and Encope. They bave the whole system low, the 

 teeth, of which the 1 and 4 surpass the 2 and o, long. high 

 and compressed, curved inward, reelining at an angle of 10° 

 to 15°; the symphysis not lunate but broadening adorally, 

 the epiphysis diminished, the arrow-shaped form developed; the 

 wings highly lamellated aiul lacunal. The ambulaera are 

 nearly uniform; in the young animal they give free space to 

 the continuous sequence of the interradia. but in the adult 

 interrupt them more or less in the trivium, while the se- 

 quence of the 5 is retained. 



In these two groups the tirst plate of every interradiiim 

 maintains its plaee in the adult, and bears the auricle, the 

 branches of wliieh are coalesed into one pieee. 



The genus Arachnoides stånds al one. The whole system 

 is low and signally stellate. The teeth, of whieh the 2 

 and o surpass the 1 and 4 in size, are high. almost straight 

 or slightly eurved inward, reelining at an angle of 16°; 

 the pyramid is excpiisitely arrow-shaped; the symphysis is ex- 

 panded su1)labially, but much more so above and outward, 

 forming a hump; the forked crest renders the alveolar anibi- 

 tus u)iconformable; the rotula is elaborate; the outer wing is 

 produced, lanceolate; the inner wing very short. The auricles 

 rise from the ambulacrum with separate branches. All t bis, 

 combined with the great preponderance of the ambulaera, even 

 to suppressing the iirst plate of the four interradia and ex- 

 cluding that of the 5 from the peristome, gives the genus a 

 highly neonomous character. 



With the Arachnoides, its orbicular and depressed test and 

 Hat ventral surface, and the eminenth' stellate form of its dental 

 system, the genus Clypeaster contrasts by its oblong test, its pen- 

 tagonal system, by the peristomal region being strongly drawn 

 in into the ventral surface at an angle of 45°, b}' the position 

 and form of the teeth. But it agrees with Arachnoides in its 



