INVERTEBRATES. 359 



top is highly elevated, standing out conspicuously over the adjoin- 

 ing parts. Even in height it extends beyond the limits of the other 

 parts of the body. 



Anal aperture large, oval in form, horizontal in position. Toward 

 the outer side the opening is formed by the wall of the anal plate, 

 which at the upper end is bulging outward without being excavated. 

 The lateral sides of the aperture are formed by the upper curved 

 ends of the oral side-plates, which are connected by two or three 

 small anal vault pieces, and these constitute the upper boundary of 

 the aperture. 



Ambulacra long, narrow, linear, raised above the general level of 

 the body, except close to the oral pole, near which they curve 

 abruply toward the oral opening, and the ambulacrum becomes lo- 

 cated below the abutting surface. The lancet-piece is deeply grooved 

 along the median line, and when the side-pieces (pore-pieces of 

 Eoemer) are not in place, there is at the suture, along each side of 

 the plate, a deep sulcus, penetrated by the hydrospire-pores. This 

 sulcus, however, when the side-pieces are in situ is totally filled, 

 and the sides of the ambulacrum rise abruptly above the abutting 

 edges. The side-pieces rest against the upper face of the deeply 

 crenulated ridges of the lancet-piece. They are strongly wedge- 

 shaped and placed obliquely to the ambulacral or food-groove, with 

 the smaller angle directed to the ab-oral side. Their number is from 

 about sixty to nearly ninety in very large specimens. The outer 

 side-pieces (supplementary pore-pieces of Eoemer) are comparatively 

 large, their longer side being about two-thirds, their shorter sides 

 fully one-half of the corresponding sides in the pore-pieces. 



The summit is a fiat disc, somewhat depressed in the middle, 

 sub-pentangular in outline, the angles resting against the slightly 

 truncated upper part of the oral plates, leaving in the direction of 

 each ambulacrum a good sized -passage. The central aperture is 

 pentangular, rather deeply depressed. 



Spiracles ten, one to each side of the ambulacrum, those of the 

 posterior side not in contact wifh the anal aperture. They are in 

 this species not easily detected, being placed laterally within the 

 projecting edges of the orals, which for their reception are at this 

 place more prominent, and somewhat excavated. The hydrospires 

 are arranged in ten groups, with two in each group; they are in 

 form similar to those of Granatocriiius Norwoodi, but comparatively 

 a little larger. Hydrospire-pores small, and more or less hidden. 



