506 T. A. STEPHENSON 
only. Not only have the Gonactiniidae a good deal approximat- 
ing them to this ancestor, but also there are no other forms of 
this grade which can fairly be placed in the same family with 
them. It seems that the family must be looked upon as one 
apart, and representative of past things; the remaining ques- 
tion, which will receive attention later, being the rank of the 
group to which it must be allocated. 
§ B. Boloceroides. 
This is a genus of uncertain affinities and needs unusually 
careful placing. Carlgren has thought of it as a Gonactinud, 
and others as a Boloceroid. It certainly does not come within 
the Gonactiniidae as understood in Section A, nor even near it. 
The characters by which it may be defined, those which most 
affect us at the moment, are as follows. (1) There is a definite 
base, but (ii) no basilar muscles. The body is (iii) smooth with 
unspecialized margin. (iv) There is no sphincter. (v) There 
is ectodermal muscle in the body-wall. (vi) Spirocysts are 
present in the body-wall ectoderm. (vil) The tentacles are 
deciduous. (viii) Six pairs of mesenteries are perfect. (ix) The 
mesenteries are not divided into macro- and microcnemes. 
(x) There are ciliated tracts on the filaments, but (xi) no true 
siphonoglyphes. 
Of these characters, the genus shares nos. i to vi and ix 
and xi with the Gonactiniidae. Character vu turns up also 
in Bolocera and Bunodeopsis, and need not trouble 
us, because it 1s a special feature which may be taken as a 
convergence—not necessarily a token of relationship with 
Bolocera, and certainly not with Bunodeopsis. 
Characters viii and x are the two of importance in which it 
differs from the Gonactiniidae, but they are rather funda- 
mental. Boloceroides represents a _ different stage 
altogether, by its possession of ciliated tracts and its attain- 
ment of pairs of perfect mesenteries, although at the same 
time it retains several primitive traits. It shares five characters 
(i, ili, vili, ix, x) with the genus Myonanthus (a form 
which, as will be seen, requires special consideration), but 
