MELOCRINID^. 321 



Dolatocrinus excavatus W. and Sp. (nov. spec). 

 Plate XXV. Fig, 1, and Plate XX VI. Figs. 7 and 8. 



A very large species. Dorsal cup shallow-basin shaped, three times as 

 wide as high ; the bottom flattened to the top of the costals ; the sides 

 convex, rapidly curving upwards, a little constricted at the arm bases ; the 

 radials formed into a deep, sharply pentangular, funnel-shaped pit, which 

 penetrates the calyx almost to the height of the arm regions. Surface of 

 plates — except those in the pit — covered with parallel ridges, radiating 

 from the centre of the plates to their sides, w^here they meet with similar 

 ridges from adjoining plates. In addition to these ridges there are keel-like 

 projections following the radials and costals, which grow more conspicuous 

 downward, and at about the top of the radials are produced into a tubercle, 

 which projects into the funnel-shaped pit, and gives its upper margin a 

 slightly stellate outline. Occasionally the carinate ridges are continued to 

 the higher brachials, but, as a rule, they become obsolete above the second 

 costals. Suture lines slightly grooved. 



Basals elongate ; forming together with the radials a highly elevated 

 inverted cone with a large pentalobate canal. Radials large, once and a half 

 as long as wide ; four fifths of the plates taking part in the pit, the other 

 fifth bending abruptly outward -, upper sloping faces short ; the lower faces 

 equal to one half the greatest width of the plates. First costals small, twice 

 as wide as long, their upper and lower faces convex. Second costals wider 

 than Jong and slightly wider than the first. Distichals four; the first as 

 large as the two costals together. Arms two to the ray, about equidistant. 

 First interbrachial slightly curving, larger than the radials and first costals 

 together, elongate, widest across the middle of the plate ; angular at both 

 ends ; the lower end bending inward so as to form a part of ih^ pit. There 

 are two large plates in the second row, three smaller ones in the third, and 

 these are succeeded by a row of six elongate pieces in the ventral disk, and 

 two additional larger plates which abut against the orals. Interdistichals 

 one or two in the dorsal cup, followed by five or six small pieces in the 

 tegmen, and a larger one between the secondary radial dome plates. Slits 

 six to each interradial space, and four to each interdistichal one. Ventral 

 disk depressed, slightly tumid; the interambulacral spaces flattened, and 

 sometimes a little depressed, producing indistinct ridges along the ambulacra. 



41 



