164 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 arez, 
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 Hehinothuria was the first deseribed, 
I have felt justified in naming the family the Echino- 
thuridee. 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 Von 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 
