REPORT ON THE POLYZOA. 
157 
The rostriform avicularium in this case differs essentially from that in the preceding 
species, in its being apparently simply a development of an original true mucro and not 
a subsequent growth altogether below the orifice. The minute structure of the ectocyst 
is very remarkable. At first sight, with a magnifying power of about 50 diameters, the 
appearance is something like that of “ crackling ” china, which is apparently due to the 
wall being constituted of exceedingly fine calcareous fibres, forming a sort of felted 
texture not unlike that of a spider’s cocoon. 
(6) Mucronella bisinuata, Smitt (sp.) (PI. XIX. fig. 5). 
Escharella bisinuata , Smitt, Florid. Bryoz., p. 59, pi. xii. fig. 229. 
Character. — Zoarium thick, coarse looking, expanded. Zocecia subserial, irregularly 
quincuncial, broadly ovate or subrkomboidal in front, oblong posteriorly; the wall is seen to 
be punctured when the thick epitheca is removed. Orifice coarctate, lower lip straight, with 
two lateral incisions. Many of the zooecia with four avicularia, two on the sides near the 
orifice and two lower down on the front ; (mandibles acute, slightly curved and pointed in 
various directions). Sometimes only one avicularium and occasionally none, especially in 
the zooecia towards the growing edge. On the dorsal aspect, the wall is thin, smooth, 
slightly convex and presents a rounded oval or reniform opening with a slightly raised 
border. Ooecia inapparent. Zooecia about 0' /, 02 wide. Operculum 0"'012 x '01. 
Habitat. — Station 190, lat. 8° 56' S., long. 136° 5' E., 49 fathoms, green mud. 
[Gulf of Florida, 9 to 19 fathoms, Pourtales.] 
There appears no reason to distinguish this form from that described by Prof. Smitt, 
the only differences between them being that in the present the zooecia in front are 
not so decidedly rectangular and that the number of avicularia is occasionally much 
greater, Prof. Smitt ascribing only one to his species, whilst in the present the number 
is very often four to each zooecium. I have been unable to discern any ooecia in the 
Challenger specimens, and consequently no character derived from them is afforded. 
The double notching of the lower lip is a striking character possessed in common by the 
two forms, and as it is of extremely rare occurrence among the Polyzoa, must be held as 
of great importance, at any rate as a specific character. 
(7) Mucronella castanea, n. sp. (PI. XIX. fig. 6). 
Character. — Zoarium flat, expanded. Zooecia rhomboidal or subovate, wide, slightly 
convex in front ; surface shining, uneven ; wall punctured. Orifice coarctate ; lower lip 
bluntly mucrou ate; peristome neither thickened, nor raised; usually an avicularium on 
one or both sides of the orifice in front, varying much in size, from 0 //- 005 to '02 in length : 
