NOTES ON L.M.B.C. ASTEROIDEA. 233 
following account of the stractures upon which my interest 
has been chiefly centred more intelligible. 
The majority of the Asteroidea assume the form of a 
five-rayed star, but in some few genera (Solaster, Brisinga) 
the rays are more numerous. Other genera (Asterina, 
Porania) are pentagonal. Except in Brisinga, a form 
which has not yet been found in our area, the rays are 
not sharply marked off from, but are continuous with the 
central disc. The oral face of each ray presents a deep 
sroove, the ambulacrum, in which the tube feet are lodged. 
The mouth always occupies the centre of the ventral sur- 
face of the disc, and is surrounded by a membranous 
peristome. It opens directly into a capacious stomach, 
divided by a deep constriction into a wide cardiac and a 
shallow pyloric portion. The walls of the former extend 
a short distance into the cavity of the rays as cardiac sacs. 
The pyloric portion is, in the five-rayed species, of penta- 
gonal form, the angles of the pentagon being radial. 
Tubular prolongations of the pylorus arise at each angle, 
- and entering the rays, from the aboral walls of which they 
are suspended by mesenteric folds, each one divides into 
two parallel and densely sacculated portions which termin- 
ate blindly near the tips of the rays. An aperture in the 
centre of the aboral face of the pylorus, closed by valvular 
folds, opens into a very short and inconspicuous intestine, - 
which has in connection with it a lobulated cecum. In 
some species a minute anal pore opens upon the aboral 
face of the disc. 
What I have already referred to as the hemal system 
consists of an elongated plexiform body, often spoken of 
as the heart (Pl. XX XVIII, fig. 2; Pl. XXXIX, fig. 1, c.pl.), 
which lies in close proximity to the water tube (wd), 
and communicates with similarly constituted circum-oral 
- (cohr) and aboral (ahr) rings. From the former plexiform 
