NOTES ON L.M.B.O. ASTEROIDEA. 139 



following account of the str:ictures 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 {Aster ina^ 

 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 

 groove, 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 csecum. In 

 some species a minute anal pore opens upon the aboral 

 face of the disc. 



What I have already referred to as the haemal system 

 consists of an elongated plexiform body, often spoken of 

 as the heart (PI. XXXVIII, fig. 2 ; PI. XXXIX, fig. 1, c.pl), 

 which lies in close proximity to the water tube {lot)^ 

 and communicates with similarly constituted circum-oral 

 {colir) and aboral {cclir) rings. From the former plexiform 



