ECHINOIDEA 297 



Only every second (or less) of the interambulacral plates on the 

 upper side with a primary tubercle. Primary spines rather 

 small, greenish. Test globular, of a brownish tint ; grows to 

 a very large size .... 4. Ech. melo Lamk. 



3. Test white, globular ; tubercles (spines) rather scarce ; small 



spines on the buccal plates . 2. Ech. tenuispinus Norman 



Test more or less conspicuously coloured with red or greenish 4 



4. Test more or less globular, mostly uniformly red, tubercles white ; 



secondary tubercles (spines) numerous, of about the same size 

 as the primaries ; small spines on the buccal plates 



1. Ech. esculentus Linn. 

 Test more or less conical, often flattened ; the red colour not 

 covering the whole test, but interrupted by white, vertical 

 bands, or the red is confined to a small patch in the inter - 

 ambulacra near the apical system. Secondary tubercles 

 (spines) usually distinctly smaller than the primaries. No 

 spines on the buccal plates . . 3. Ech. acutus Lamk. 



5. Primary ambulacral tubercles form regular, equal-sized series 6 

 Primary ambulacral tubercles either of very unequal size, or, if 



decreasing regularly in size towards the apical system and the 

 peristome, the two series in each ambulacrum of very unequal 

 size. Test white. Tridentate pedicellarise very slender 

 (Fig. 167, 5) 1, Ech. afflnis Mrtsn. 



6. Test usually low, conical or arched ; generally with a more or 



less distinct trace of red or violet colour ; spines often beautifully 

 red with white tips. Globiferous pedicellariae usually with 

 2-3 lateral teeth ; tridentate pedicellarise with rather narrow 

 valves (Fig. 167, 2) . .5. Ech. elegans Diib. and Kor. 



Test usually flattened above ; colour white or (the skin and 

 spines) a faint reddish -yellow. Globiferous pedicellarise usually 

 with 3-4 lateral teeth ; tridentate pedicellarise with broad 

 leaf -shaped valves (Fig. 167, 1) 



6. Ech. Alexandri Dan. and Kor. 



1. Echinus esculentus Linnaeus. (Fig. 168.) 



(Syn. Echinus sphcera 0. Fr. Miiller.) 



Test usually globular, more rarely somewhat depressed or 

 subconical. It is rather closely covered wdth short spines, among 

 which the primaries are scarcely conspicuous ; in correspondence 

 with this the primary and secondary tubercles are of about the 

 same size, and the longitudinal series of the primary tubercles 

 very indistinct. This, however, holds good only for the larger 

 specimens ; in the smaller specimens the secondary spines and 

 tubercles are not so large as the primaries, and the longitudinal 

 series of the latter, therefore, are fairly conspicuous. Only every 

 second or third ambulacral plate carries a primary tubercle. 



