THE DEPTHS OF THE SEA. [CHAP. iv. 



essential family characters they agree. The plates 

 imbricate in the same directions and on the same 

 plan, and the structure of the ambulacral arese, 

 which is so special and characteristic, is the same 

 Echinothuria differs from Calveria in the wider inter- 

 ambulacral and ambulacral plates, in the smaller 

 amount of overlapping, and in the absence of mem 

 branous intervals; and from Phormosoma it differs 

 in having the structure and ornament of the apical 

 and oral surfaces of the test the same. 



As the genus Echinothuria was the first described 

 I have felt justified in naming the family the Echino 

 thuridse. I have done this with the greater pleasure 

 as it brings into prominence a term suggested by 

 my late friend Dr. Woodward, whose early death 

 was a serious loss to science. In Dr. Woodward's 

 memoir, the following curious paragraph occurs : 



" After this apparently conclusive demonstration, 

 it appears desirable to give a name to this fossil and 

 to attempt a short description, although its rank and 

 affinities are still a matter of conjecture. At present 

 it is one of those anomalous organisms which Milne 

 Edwards compares to solitary stars belonging to no 

 constellation in particular. The disciples of Yon Baer 

 may regard it as a ' generalized form ' of echinoderm, 

 coming, however, rather late in the geological day. 

 The publication of it should be acceptable to those 

 who base their hopes on the ' imperfection of the 

 geological record,' as it seems to indicate the 

 former existence of a family or tribe, whose full 

 history must ever remain unknown." The special 

 bearings of the discovery of this group, and of 

 several other animal forms allied to chalk fossils 



