ECHINOIDKA. I. 



J 43 



Agassi z: Revision of Echini, p. 491. -- Wyv. Thomson: Echinoidea of Porcupine > (395) p. 744. - 

 Hoyle: Rev. List of Brit. Echinoidea (202) p. 414. Bell: Catalogue of Brit. Echinoderms. p. 154. 



The form of the test rather varying, from evenly rounded to slightly conical, on the actinal 

 side evenly rounded or almost flat (in the conical forms); the edge of the mouth always somewhat 

 bent inward. The peristome rather large. The height of the test a little more than half the diameter; 

 the contour round. 



The ambulacral areas (PI. XVI. Fig. 19) a little more than half as broad as the interambulacral 

 ones, at the edge of the mouth generally a little broader than the latter. The number of ambulacral 

 plates is rather constant, one third as great as that of the interambulacral plates. The boundaries 

 between the primary plates generally somewhat indistinct; the boundary line between the areas not 

 much sinuate. The arcs of pores rather steep; the pores reach quite to the edge. Sometimes four 



All the measures are in millimetres. 



pairs of pores are found in an arc. The primary tubercles are rather large and strong, somewhat 

 smaller than the interambulacral ones, and form a very conspicuous, uninterrupted longitudinal series, 

 a primary tubercle being found on all the plates. They are placed very close together, the edges of 

 their scrobicular areas join through almost the whole area only the very uppermost ones are sepa- 

 rated. This fact of the tubercles being placed so close together gives to the test a very charac- 

 teristic appearance. The secondary tubercles may form a short longitudinal series on the actinal side 

 inside of the primary series, but this feature is not a constant one. On the abactinal side there are 

 only few secondary tubercles; commonly there is one small tubercle between the pores and the prim- 

 ary tubercle. Miliary tubercles numerous and rather strong; together with the secondary ones they 

 give the whole test a very rough and uneven appearance. (In the figures the miliary tubercles have 

 been omitted.) 



The interambulacral areas (PI. XV. Fig. 4). Also here the primary tubercles form a very close 

 series, the scrobicular areas, however, do not join above the ambitus. The secondary tubercles are 

 very numerous on the actinal side; they are considerably smaller than the primary ones, and form 

 no distinct longitudinal series neither inside nor outside of the primary ones. 



The apical plates carry rather many tubercles (PI. XVI. Fig. 3). The periproct is generally very 

 small (in the figured one it was larger than is commonly the fact), covered by numerous, irregular 



") The specimen figured on PI. I. Fig. 2. 

 2 ) The specimen figured on PI. I. Fig. 3. 



