EIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 18. AFD. IV. N:0 I. 



37 



gronp consisting, besides, of tlie genera Boletia Ag. and Lyte- 

 chinus LuTKEN. 



In tlie Diadema saxatile L., wlien an aurienlar arch is 

 viewed half sidewise from behind, tliat is from tlie cavity of 

 the test: fig. 1; from before, tbat is from the stoma: fig. 2; oy 

 from behind: fig. 3; or sidewise: fig. 4; tbe snture a, h, c, marks 

 the extent of the adhesion of the basilar expansion of the an- 

 ricle to the ambulacrnm. From a to a' and from a' to b it 

 denotes the continuation of the raain snture between the am- 



1. 



4. 



Auricle of Diadema saxatile L. 



bnlacrnm and the interradium, which diverge at h, so as to 

 form each of them one side of the branchial incisnre. In the 

 four fignres the sutnre a, b. c niay be followed all around, on 

 the ambolacrnm. In fig. 1 it presents between a and c a very 

 irregular, projeeting and receding conrse, the thinned edges of 

 the expansion of the anriele being conspienonsly lacerated. 

 This is because in this genus there are found here and there 

 on the inner snrface of the ambulacral plates isolated, more or 

 less pointed knobs, analogous, perhaps, to the arcuated projec- 



