vni PHYLUM MOLLUSCOIDA 353 



the future animal ; the larval tentacles and pre-oral lobe are thrown 

 off, and the lophophore is developed. 



The Phoronida have a wide geographical distribution, occurring 

 in all the chief regions. Some of the species live about low- water 

 mark : others at moderate depths up to about thirty fathoms. 

 Some of the associations take the form of encrustations of the 

 matted tubes. In other cases the tubes lie in excavations in stone 

 or in the shells of Molluscs. In one species the tubes occupy 

 channels in the substance of the tube of a Sea-anemone. 



CLASS III.-BRACHIOPODA. 



The Brachiopoda are the fabricators of the well-known " Larnp- 

 shells " found in most parts of the world. They occur in the sea 

 at various depths, and were formerly classed under the Mollusca, 

 their characteristic bivalved shell being compared with that of 

 oysters, mussels, &c. 



1. EXAMPLE OF THE CLASS Magellania (Waldheimia) lenticularis 



or M. flavescens. 



Magellania lenticularis is found in great numbers, at moderate 

 depths, off the coast of New Zealand. An allied species, M. flavescens, 

 is equally common in the Australian seas, and several other species 

 are known in various parts of the world. 



The body is entirely covered by a shell (Fig. 295) of oval form 

 and pink colour, composed of two pieces or valves, one of which, dis- 

 tinguished as the ventral valve (v. v), projects beyond the other 

 or dorsal valve (d. v), in the form of a short conical beak (b) perfor- 

 ated at the end by an aperture, the foramen (b), through which 

 passes a dark brown stalk or peduncle (Fig. 296, B, pd) of horny 

 consistency. In the natural state the peduncle is attached to a 

 rock or other support, and the animal lies with the ventral valve 

 uppermost and with the valves gaping slightly. The pointed or 

 peduncular end of the shell is considered to be posterior in position, 

 the opposite end or gape anterior. 



It will be convenient to consider the shell first. Both valves are 

 deeply concavo-convex, of a pinkish or brown colour outside, white 

 within. The ventral valve (Fig. 295), as already stated, is produced 

 posteriorly into a beak (6), terminating in a foramen (/) for the 

 peduncle. The distal margin of the foramen is left incomplete by 

 the shell proper, but is closed by a small double plate, the deltidium 

 (d). Immediately anterior to the beak is the curved hinge-line 

 along which the valve articulates with its fellow, and just anterior to 

 the hinge-line the inner surface of the shell is produced into a pair 

 of massive, irregular hinge-teeth (t). On the inner surface of the 

 valve, towards its posterior end, are certain shallow depressions 

 marking the attachments of muscles (ad.m, d. ni). 



VOL. I. A A 



