MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTERID2E. 447 
to the surface of the embryo all over, and this condition is very conspicuously marked 
in the fully-developed planula (Plate 37, E C). The mature planula is elongate-ovoid 
in form, and is slightly folded once upon itself in order to accommodate itself to the 
confined space within the ampulla. The layer of ectoderm described as investing the 
surface of the ovum and derived from the spadix, persists as a covering of the mature 
planula until set free (Plate 37, B). 
In line sections of mature pi arm he the line structure of the ectoderm and endoderm 
is well seen. The ectoderm forms a thick layer composed of alternately placed 
transparent and opaque tracts disposed vertically to the surface of the planula. The 
more opaque tracts contain numerous nuclei and thread cells in process of development. 
The dark tracts fuse together towards the inner region of the layer, and form a con- 
tinuous mass full of nuclei which rests upon the basement membrane, as yet little 
differentiated but still clearly indicated (Plate 44, fig. 9, B). 
When the planula is viewed from the surface the transparent areas of the ectoderm 
are seen to be enclosed by the opaque tracts which spread round them : a condition 
more clearly marked in the case of the planuke of Cryptohelia. 
The endodermal mass of the planula is composed of much granular matter, in which 
are embedded numerous small transparent cells and nuclei, also oil-globules of various 
sizes, and many nematocysts in various stages of development (Plate 44, fig. 9, E N). 
(4.) GENUS SPINIPORA, Gen. Nov. (H. N. M.) 
Amongst the other Stylastericlse obtained off the mouth of the La Plata in GOO 
fathoms, was a single specimen of a form to receive which I have made a new genus, 
Spinipora. It is closely allied to Errina, but shows sufficient differences in the 
structure both of the hard and soft tissues to warrant its being placed, at present at 
least, in a separate genus. 
Corallum of Spinipora echinata. 
The corallum (Plate 34, fig. 3) is in the form of a single irregularly cylindrical stem, 
bearing at its summit, in the only specimen procured, a couple of similarly shaped 
branches. The base of the stem is somewhat swollen, and encrusts the object to which 
it adheres. The whole surface of the corallum is thickly beset with spinous pro- 
jections which being all inclined towards the tips of the branches stand out beyond 
the main surface of the stem to a distance of as much as one-tenth of an inch, the 
diameter of the stem itself being about three- tenths of an inch. The spines are spout- 
like in form, more or less conical, with the ends usually truncated, and their upper 
surfaces — that is, those turned towards the tips of the branches — channelled out into 
deep and wide grooves. The grooves usually commence on the surface of the spines 
as slits, and widen out to terminate at the truncate ends of the spines in wide spout- 
like mouths. The groove-like excavations are continued as tubular cavities for a short 
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