BIIIAXG TILL K. SV. VET.-AKAD. IIANDL. BAXD 13. AFD. IT. N:0 5. 99 



Tlie series are seen to follöw each other regularly, the 

 låter of them being only very slightly retarded. The faint 

 indication of a står in the non-adult specimens comes from 

 tlie temporary smallness of the tubercles of the fifth and sixth 

 series. It disappears entirely in the adult. The mesial lan- 

 ceolate space is distinct; it contains the few minitte tubercles 

 of the seventh series, Tah. 3, fig. 3. 



The ainbiilacral tubercles are somcwhat smaller than the 

 corresponding interradial ones. Above the ambitus they se- 

 parate so as to leave between their scrobicular circles a dis- 

 tance equalling the half part of one circle. Ventrally the 

 iirst four pairs are rather close together, while upwards, above 

 the ambitus, the tubercles of either series become more and 

 more sparse, till ucar the top one of the two series alone 

 continues or surpasses the other in tlie size of its tubercles. 



The epistroma is largely developed. In the specimen a 

 the interradial tubercles, up to the fifth or sixth, cover with 

 their bases the entire height of their plates so as to leave 

 very little room for its globular granules, but on the sixtla. 

 or seventh plate from below and the following, Tah, 7, jig. 7, 

 the aboral part becomes more and more free and is occupied 

 by an assemblage of conspicuous, glossy, semi-pellucid, rounded, 

 slightly deformed, vmequal, sub-pedunculated projections closely 

 ovcrhangiug the scrobicular circles, penetrating between them 

 and re-appearing at the adoral margin. Laterally, above the 

 tubercles of the two or three hrst series, they take the shape 

 of lengthened vertical swellings; towards the inner end of the 

 plate they diminish and become less densely packed, leaving 

 nearly bare a small triangulär sutural space. This is where 

 the tubercles are all developed. On the upper plates of the 

 non-adult specimens, where the tubercles are still forming or 

 delicicnt, they inwardly diminish into slightly raised knobs 

 densely coalesced into a swelling layer and disposed into more 

 or less conspicuous transverse rows radiating towards the su- 

 turcs or more or less directed towards the middlc suture, 

 Tah. 7, /?'</ 2. In the calycinal system of the adult the epi- 

 stroma takes this form, and its striation, from its hiojhest part 

 on each costal, half way between the pore and the periproct, 

 is directed divaricatiugly towards the margin. On the zone 

 of pores its large glossy granules appear on the sutural and 

 aboral margins of eacli demi-platc, and on the compound plate 



