BIHANG TILL K. SY. VET.-AKAD. HANDL. BAND 18. AFD. IV. NIO 1. 33 



iiieaiis of an uninterrupted sequence of pedicelligerons ambnla- 

 cral plates, persists, seemingly at least, in the adult. -while in 

 the other genera of the group the traces left hy reabsorbed 

 ambulacrals in the large circular belt between the primordials 

 and the peristouie, are plainly reeognized nnder the form of 

 five anibnlaeral areas. The interradials are mnch less distinct. 

 Among the other Ectobranchiates. while anything closely re- 

 sembling the disjDOsition in the Diadematidfe is hardly ever 

 niet with, the calcified particles of the bnccal merabrane are, 

 however, generally more or less j^ilainly distribnted, numerously 

 into five anibnlaeral groups, and sparingly into five interra- 

 dial. In the Eehinns escnlentus L. P/. XII, fig. 156, the 

 calcified particles are of two sorts: minnte, almondshaped, 

 transverse, glossy, snbnierged in the niembrane. and others 

 raised above it, fewer, larger, convex, ovoid, verruculated, as- 

 sembled in groups, in front of the gills and thence to the 

 outer sides of the primaries, and in the middle. In front of the 

 interradia there are none, or very few and minnte particles. 

 In the Eehinns angulosns Leske the snbnierged particles are 

 numerons, very minnte, the raised ones fewer, larger, ronndisli, 

 forming two groups in front of each ambulacrum, between the 

 peristome and the primordials. The narrow interradia! areas 

 have only verv niinute corpuscles. — The Echiiiometra Mathsei 

 Blv.. Fifi. 157, has the snbnierged spicules very minnte and 

 slender, somewhat larger and densely crowded along the middle 

 of each anibnlaeral area; the raised corpuscles small, ovoid, 

 sparse, but forming two somewhat marked groups from the 

 gills to near the primaries; the snbnierged spicules of the in- 

 terradia are very minnte. — In the Tripneustes Gratilla L. 

 there are no snbnierged corpuscles and the raised ones are 

 sparse, minute, rounded, clustered at the gills and about the 

 middle of the area. and a few larger. flattened, between the 

 primordial pairs. — The Lytechinus semitnberculatus Val., 

 Fig. 158 has the entire niembrane densely covered with flat- 

 tened, niostly rhomboidal, plate-like, centrally verruculated 

 laniinpp, larger in front of the anibulacra, from the gills to 

 outside each primary pair. smaller and less crowded in the 

 triangulär interradial area, minnte near the peristome. — In 

 the Echinocidaris nigra MoL., Fig. 159, it is hardly possible 

 to make ont any order among the thickly strewed, raised, mi- 

 nute corpuscles, each with the large conical verruca for a for- 



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