BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 18. AFD. IV. NIO 1. 51 



As far as I liave been able to make ont the structure of 

 these parts in the other genera of the Echinoconidse, it seems 

 to be essentially the same in all. In the Pygaster semisulca- 

 tus Phill.^ the five or six first plates of both colnmns in each 

 ambnlacrnm expand laterally, while the poral zones converge 

 and at the same time become gradually higher so as to form 

 by their snccession two ridges rising adorally and terminating 

 with a slightly concave surface that descends rather steeply 

 toward the peristome. The section shows the gradnal increase 

 in height of the ambnlacral plates 8 to 1, and their ending sur- 

 monnted by an overhanging projection which seems to come 

 into view between the tops of the two first ambnlacrals. The 

 same appears to hold good in Holectypus. In the Anortho- 

 pygns orbicularis Cotteau the raising np of the compressed 

 peristomal plates of the ambnlacrnm is very distinct, as is also 

 the sntnre between them and the interradinm, which, as by 

 rnle, forms the greater part of the branchial sinns. Thanks 

 to the kind liberality of M. Cotteau I have been able, by ta- 

 king a cast of a specimen of Pilens hemisphsericus Desor- in 

 liis collection, to convince mj-self that the same structure main- 

 tains also in that genus. 



' When the anriciilar system thus described is compared 

 with that in any other among the Regnlaria, a striking dif- 

 ference is found in the smallness of the stoma in proportion 

 to the diameter of the test. In those gronps this was found 

 to vary between O, .5 9 and 0,2 2 of the total diameter, in the 

 Pygaster semisulcatus Phill. it is 0,2 1 of the same, in the 

 Galerites Albogalerus Leske 0, 13, in the Discoidea cylindrica 

 Lamck 0,10. The loss of substance through reabsorption at the 

 peristome is also less; in all the five interradia of the adult 

 Pygaster semisulcatus,^ Holectypus depressus Leske,* Discoidea 

 cylindrica,^ the solitary first plate is preserved to no small 

 extent. At the same time the distance between the opposite 

 tops of two auricles is, in the Discoidea, 0,2 4 of that of the 

 test, while the diameter of the stoma is 0, 10. In the Diadema 

 saxatile L. the same measures are 0,6 o and 0,4 8; in the Echi- 

 nus esculentus 0,3 3 and 0,2 4, in the Echinometra Lucunter L. 



' See my paper on a recent form of the Ecliinoconidte, p. 7, fig. 12, 13. 

 ^ Paléontologie frau^aise, Terrain Jurassique, IX, pl. 115, fig. 1. 

 ^ On a receut form of the EchinoconidEe, Pl. 2. fig. 12. 

 •* Etudes sur les Echiiioidoes, Pl. XIV, fig. 124. 

 •■* See woodcut, pag. 4b. 



