ENCOPE EMARGINATA. 327 



anal opening are separate, the latter being placed at a considerable distance 

 from it toward the mouth. As the specimens become older there is a ten- 

 dency to separate, the anus being placed in a groove which is a shallow con- 

 tinuation of the lunule, approaching more and more the mouth, till, in 

 specimens measuring 37."™ in diameter, the anus is completely separated 

 from the lunules (see Pi. XII. f. is, 21, 23, 25). The shifting position of 

 the anus depending upon entirely individual circumstances, shows that 

 its position cannot be used as a specific character. The youngest Encope 

 I have had occasion to examine shows already traces of the two posterior 

 ambulacral notches (PI. XII. f. U h 15), but they are so slight that they 

 would most likely be overlooked, especially in specimens somewhat more 

 advanced, when the scalloping is more pi'ominent (as in the figures of 

 Moulinsia of Agassiz in his Monographic des Scutelles), in fact, the cuts of 

 the edges being fully as deep as the notches. These divide the edge of the 

 test into twenty well-marked scallops, the ambitus is elliptical, the apex cen- 

 tral, and in this condition the ambulacral and interambulacral plates both 

 diminish gradually in size towards the centre, forming twenty sharply defined 

 ridges, the sutures between the plates running to the apex from the edge 

 of the test being well marked by the absence of granulation. Each ambu- 

 lacral and interambulacral plate carries from one to two, or at most (near 

 ambitus) three, primary tubercles, the rest of the plate being covered by 

 miliaries. There is no ambulacral rosette, but two pairs of pores; one pair, 

 between adjoining ambulacral plates, extend in each poriferous zone from the 

 apex to the ambitus, there being in the present stage only as many ambu- 

 lacral as interambulacral plates (PL XII. f. 14), seven from ambitus to apex. 

 There is a faint trace, even at this early stage, of a madreporic body, but no 

 genital openings are as yet formed. The pairs of pores are not } r et con- 

 nected by a furrow, but are simple holes. The furrows formed by the 

 sutures of the plates are not as deeply cut on the lower surface, those of the 

 median ambulacrum being most prominent; the position of the poriferous 

 furrows is indicated by minute pores irregularly scattered, while towards 

 the mouth at the base of the furrows the pores are quite large, forming 

 almost an imitation phyllocle. The rotules, on each side of which start the 

 lines of pores, are already apparent. The lower surface is concave, the 

 edge being slightly raised ; the outline seen in profile is somewhat more 

 convex than in older Encope, but the difference bears no comparison to the 

 difference noticed in young Echinarachnius. 



