128 SVEN LOVEN, ON THE ECHINOIDEA DESCRIBED BY LINN^US. 



marginal tertiaiy tubercles 

 on the interradia is seen 

 in all the Diadematidse. In 

 Centrostephanus therc are 

 three such series between 

 the zone and the primor- 

 dial series of tubercles. 



It is readily seen that 

 LiNN^^us regarded the Echi- 

 niis Diadema as the prin- 

 cipal species of the two, 

 and that he first drew up 

 Part of the ambulacrum of E. Diadema. itS description from the 



showiag the lateral series of larger Ijn-aer and more instnic- 

 tertiaries. , '^ 



tive specimen, and then 



that of the other, the E. saxatilis, treating this less circum- 

 stantially and rather summarily. He says it closely re- 

 sembles the E. Diadema, but is of a smaller size. Its pri- 

 marv tnbercles he describes as formino- four, not six series 

 in every interradium, but »castera eadem», that is: their ma- 

 melons are perforated as in that species. From this cha- 

 racter, which is set down as common to both, being distinc- 

 tive of the Diadematidse ; from the resemblance of the tAvo 

 species to each other insisted upon throughout, and from the 

 care that is taken to keep them jointly apart, it follows that 

 the Echinus saxatilis L. is also a member of that group. 

 While in the E. Diadema the ambulacra, that is the zones, 

 are combined by pairs iuto five »radii», convex, elevated and 

 lanceolate, they are simply counted separately as ten in the 

 E. saxatilis, the pairs only being approximated. In both spe- 

 cies the ambulacra present two vertical series of tubercles, 

 but in the interjacent space there are in the E. saxatilis two 

 series of tertiaries, not four. Unlike what is said of the pores 

 in the E. Diadema it is here stated that they are placed in 

 a double row, that is a simple row of geminous pores, and 

 are met with also on the ventral side, »subtus etiam obvii», 

 which cannot but mean that they are there arranged in the 

 same manner, or nearly so, as on the dorsal side, that is: not, 

 in diagonal rows of three pores as in E. Diadema. A dispo- 

 sition like this, in simple rows, when looked for among other 

 Diadematida3, is nowhere found under the ambitus in full- 



