88 PKOCEEDINGS OF THE M.yLACOLOGICAL SOCIETY. 



not divided into two portions as it is in Ostrea, where we find one 

 part composed of smooth, and the other of striated fibres. 



A small posterior pedal retractor {p.r. ) is present in Miilleria, situated 

 immediately above, or anterior to the posterior adductor, and exhibiting 



/ 



Fig. I. — General view, somewhat diagrammatic, of the anatomy of 



Miilleria Balyi. 



a. anus ; au. left auricle ; e.g. cerebral ganglion ; g. gills ; g.d. genital duct ; 

 g.g. genital gland ; int. intestine ; k. kidney ; I. digestive gland ; l.p. inner 

 labial palp ; m. mouth ; p. a. posterior adductor muscle ; pc. pericardium; 

 p.g. pedal ganglion ; p.r. posterior retractor pedis muscle ; p.v. parieto- 

 visceral ganglion; r. rectum; r.o. renal opening; r.p. reno- pericardial 

 aperture ; st. stomach ; t. typhlosole ; v. ventricle. 



the typical relations of that muscle to the organ of Bo j anus and to the 

 nerve-cords. 



The Mantle Cavity. — The branchial cavity is large and entirely open 

 below. The supra -branchial (anal) chamber opens posteriorly by 

 a wide slit : it consists of a large median chamber behind the posterior 

 adductor muscle, where it receives the opening of the anus. Under 



