ECHINOIDKA. I. 



143 



Agassiz: Revision of Echini. p. 491. — Wyv. Thomson: Ecliinoidea of Porcupine (395) p. 744. — 

 Hoyle: Rev. List of Brit. Ecliinoidea (202) p. 414. — Bell: Catalogue of Brit. Echinoderni.s. p. 154. 



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

 side evenh- rounded or ahiio.st flat (in the conical forms); the edge of the moutli always somewhat 

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

 the contour roimd. 



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

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

 piates is rather constant, one third as great as that of the interambulacral piates. Tlie boundaries 

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

 much sinuate. The arcs of pores ratlier steep; the pores reacli quite to the edge. Sometimes four 



.Ml the measures are in iiiillimetres. 



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

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

 a primary tubercle being found on all the piates. They are placed ver>- close together, the edges of 

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

 rated. This faet of the tubercles being placed so close together gives to the test a ver}- 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 tliere are 

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

 ary tubercle. ]\Iiliary tubercles numerous and rather strong; together witli 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 liere 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; tlie\' are con.siderably smaller than the primary ones, and form 

 110 distinct longitudinal series neither inside nor outside of the primary ones. 



The apical piates 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 faet), covered b)- numerous, irregular 



') The specimeii figured on PI, I. Fig. 2. 

 ') The specimen fij:;urfil on PI. 1. Fig. 3. 



