BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 13. AFD. IV. N:0 10. 11 



triads liaving tlie middle platc compressed and narrowed to- 

 wards the siiture, Pl. 2, jig. 11, but after only two or three 

 triads tbis tendency disappears, and both series present all 

 through none but uniformly entire and simple plates. All tlie 

 authors agree in giving such a disposition of tbe ambulacral 

 plates to Pygaster, Pilens and Anortbopygus, and it is witb. 

 these genera tbat our recent Echinoconid agrees, wbile Dis- 

 coidea is distinguislied by a bigbly developed and pervading 

 triadic disposition ^). 



It is in connexion witb tbe rcgular and uniform sequence 

 of plates tbat tbe zones of pores are simple and straigbt, as 

 in Pygaster and its allies. Tbe comma-sbaped geminous pores 

 recall tbose of certain Clypeastridas -), but also, tbougb ratber 

 distantly, tbe modification of tbe external perforation obser- 

 vable, aecording to Cotteau, in tbe Pygaster macrocypbus 

 Weight •^), and tbe Galeropygus agariciformis Forbes *). 



Tbe size of tbe tubercles is greater tban in tbe Irregulares 

 generally, it is bowever sligbtly exaggerated in tbe y?^. 1 and 2, 

 Tbe mamelon is perforated as in all tbe Ecbinoconidae and 

 many Ecbinoneidse. It is surrounded by a very distinct cre- 

 nulatiou, tbus far like wbat is seen in Anortbopygus, Holec- 

 typus, Discoidea, but difFerent from tbe mamelon of Pilens 

 and Pygaster wbicb is said always to be witbout any crenu- 

 lation. 



Tbe numerous epistromal protuberances form a very strik- 

 ing feature. Tbey present some resemblance to tbose of Ecbi- 

 noneus '") and certain Clypeastridas. Tbey were, bowever, not 

 absent in tbe old Ecbinoconidse. Tbe Galerites Albogalerus, 

 on its dorsal surface from tbe ambitus upwards presents bet- 

 ween tbe tubercles, wbicb nre tbere tbinly scattered and of 

 an inferior size, numerous minute sub-pedunculated prickly 

 epistromal globules, standing singly but assembled into more 

 or less distinct dusters on tbe several plates, wbile on tbe 

 ventral surface tbe tubercles, on becoming at tbe ambitus more 

 numerous and larger, are closely surrounded by protube- 

 rances densely pressed togetber into a swelling layer. Tbe 

 descriptions and figures given by Cotteau of species from tbe 



') Etudes 9. 1. Echinoidées. Pl. XIV, fig. 125. 



2) Ib. Pl. VIII, fig. 73, 74, 75. 



') Pal. Frang.; Jura, p. 492, Pl. 137. 



") Ib. p. 329, Pl. 86, f. 3—7. 



») Etudes 9. 1. EchinoneiYles, Pl. IX, fig. 79, 80. 



