BIIIANG TILL K. SV. VET.-AKAD. HANDL. BAND 13. AFD. IV. N:0 5. 89 



straio-ht, one of which, uearly parallel to tlie side of the peu- 

 taiion, passes över the siitvire, continues into the adjacent costal, 

 and th\is forms a side of an outer pentagon. Three or more rid- 

 gcs are carried diagonally across the sutvires into the adjoining 

 radial and directed towards a triangle formed by three somewhat 

 smaller berry-like protuberanccs, the uppermost one or two 

 converging with the corresponding ones of the contiguous 

 costal and tending to merwe into the base of the middle 

 protuberance, while the rest are directed towards another of 

 the two lateral ones that stånd above the »orbital» notches. 

 Över the projecting mesial septum the epistroma descends on 

 the ambulacrum. There it forms, at each margin of the narrow 

 areola, and bordering iipon the zone of pores, a glossy ridge, 

 which is seen to rise, on each of the plates still devoid of 

 tubercles, into an erect protuberance. On the interradia it is 

 the same; the ridges connect and rise into protuberanccs at 

 the knöts, on each half a first and lateral series, and a second 

 less numerous. The ridges are still in this early stage conti- 

 niious and cross withont the sign of a break the underlying 

 sutures which are seen through their transparent snbstance, — 

 in a few places only they are interrupted or contract a little 

 as if preparing to part. In this state the epistroma extends 

 över uearly the entire dorsal region. Four or iive protuberanccs 

 in a series may be counted in the ambulacra, three in the 

 first ambiilacral series, alteruatiug ou each side, wheu the two 

 lowest at the ambitus are approached each by a spiue and 

 tubercle rising from under the thin envelope, the newest of 

 the series as their formation advances from the veutral side, 

 and at this stage has as vet hardly transgressed the equator, 

 Tah. 8, jig. 2, Tah. ,9, /. 5. It soon passes this limit. When 

 tho two antagonistic structures meet: the reddish vitreous 

 epistroma extending from above, and from below, successively 

 forming, the highly contrasting tubercles, iiltimately to become 

 the stronger of the two, each raising its opaque-white mamelon, 

 to meet the nascent spiue, then the cone, and lastly making 

 rooin for its scrobicular circle expanding above, the epistrome 

 is seen at first to hold its own, as it were, its glomerated pro- 

 tuberanccs facino- the tubercles, but soon gives wav, until of 

 its projecting compouents verv little is seen among the large 

 tubercles. The Tah. 9, figs 1 — 4, taken from another young 

 specimen of A. aaquituberculata are made to represent the 



