SPATANGUS. 13 



Also the small fragment of an ovate, much depressed, slightly convex urchin, with 

 parallel ambulacra, a terminal vent, overhung by a projection of the back, the whole 

 surface covered by close-set, equal, minute tubercles within impressed areolae, (Plate II, 

 fig. 6,) possibly belonging to a species of Echinarachnius. 



They are both from the Red Crag. I know no urchins, living or fossil, which can be 

 compared with these curious fragments, of which I would strongly urge collectors to seek 

 for even the smallest portions, in order that some more certain clue to their relations may 

 be discovered. It is not impossible, indeed, that the one represented in fig. 6 may be 

 distinct from that delineated in fig. 8. 



They are both from the Red Crag. 



Family — Spatangid^e. 



These are heart-shaped urchins, more or less elongated and bilateral, having petaloid 

 dorsal ambulacra, a terminal anus, and an excentric mouth, covered by a more or less 

 projecting lip. They have no dental apparatus. The apical disk is perforated by four 

 genital and five ocular holes, but there is the usual number of plates going to its 

 composition. The genera are distinguished from each other by the presence, absence, and 

 arrangement of the fascioles, which are circumscribed bands of minute spines, and by the 

 presence or absence of large tubercles bearing primary spines. No genus of this family 

 has been noticed in strata older than those of the Cretaceous epoch. 



' Genus — Spatangus, Klein. 



Body depressed, cordate, with heterogeneous ambulacra converging to a genital disk, 

 which is dorsal and entire ; superior portion of the lateral ambulacra petaloid. Anterior 

 ambulacrum in a sulcus. Anus terminal; a caudal fasciole, but no dorsal one. Pour 

 genital pores. Mouth bilabiate, excentric, placed anteriorly on the ventral surface in 

 front of an escutcheon. Spines slender, curved, the primaries longer than the others, and 

 borne on large tubercles, which are especially developed on the anterior portion of the 

 dorsal surface. 



There is no true Spatangus known from strata lower than Tertiary. Most of the 

 existing species are natives of the North Atlantic. 



1. Spatangus purpureus. Plate II, fig. 3. 



Spatangus purpureus, Muller, Zool. Dan. Prod., 2850, and Zool. Dan., tab. vi. 



— — Leslce ap. Klein, p. 238, tab. 43, figs. 3 — 5 ; (see, also, Enc. 



Meth., pi. 157, figs. 1—4.) 



