BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 13. AFD. IT. N:0 5. 127 



the genus is determined by the form of the ambulacra. These 

 are broad near the peristome, narrow at the ambitus, expan- 

 ding again iipwards, so as to become inversely lanceolate, and 

 raised above the interradia. Their compound plates are ter- 

 nary, and the three geminous pores, which are disposed dia- 

 gonally in the broad, slightly concave ventral part of the zone, 

 become more longitudinal towards the ambitus, and above it 

 form faintly arched triads. On its inner side each zone has the 

 vertical series of secondarv tubercles. Ventrallv these two 

 series are N^\y closc together, leaving room for only two sparsely 

 alternating rows of granules; towards the ambitus they slightly 

 separate, the tubercles slowly increasing. Somewhat above 

 that point these begin to diminish again, and at the same 

 time to diverge from one another, while in the interjacent 

 space, the discus, which thus widens upwards and contracts 

 again only close to the »centrum», there are gradually intro- 

 duced new vertical crowded series of more minute tertiary 

 tubercles, forming transverse rows, alternating from right and 

 from left, and concealing the middle suture. The uppcrmost 

 three or four newly formed plates are bare. In the typical 

 specimen the number of small tertiary tubercles in a trans- 

 verse row across the disk, between the somewhat larger max- 

 ginal ones, increases to four. A young specimen of 40 mm. 

 has only two, a number seen also in some adult specimens, 

 but this difference hardly ought to be regarded as of specific 

 value. The broad interradia, with the large primary tubercles 

 forming at the ambitus six series, present in the narrow inter- 

 stices left by the flat cxpanded scrobicules, diminutive tertia- 

 ries in wiuding rows, of size as far as there is room. Late- 

 rally and closely bordering upon the zona is thus formed, on 

 each plate, a regular vertical series of slightly curved arches, 

 which under the ambitus become more strongiy marked, more 

 dense, and nearly straio-ht, but more irregular. With the ex- 

 ceptioa of these series there is not to be found anythiug an- 

 swering to the words of the supplemental description: »Punc- 

 torum majorum eminentium series utrique lateri radiorum 

 adjacet, subtus eadem sed scabrities minus ordinata». The ac- 

 cordance would be perfect, were it not for the word: »majo- 

 rura», — but true it is that the tubercle at the upper angle 

 of each plate is somewhat larger than the rest. The words 

 are repeated of E. saxatilis, and this same disposition of the 



