BEACHIOPODA. 79 



Localities, &c. Some species are occasionally 

 found in rock-pools, and at the verge of low water ; 

 but the depths of the sea are the proper home of 

 the BRACHIOPODA. A hundred fathoms' depth is 

 no uncommon residence for these animals ; and one 

 species, Crania per sonata, has been dredged up 

 from a depth of 255 fathoms ! 



Identification. The chief particulars to be at- 

 tended to in the identification of our recent species, 

 are the general form of the valves ; the mode of 

 their attachment; the sculpture or markings of 

 the exterior ; the nature of the hinge ; the form of 

 the shelly frame-work of the arms ; the muscular 

 impressions, or those produced by the insertions 

 of the muscles ; the vascular impressions, or those 

 which correspond on the interior of the valves to 

 the blood-vessels of the mantle ; the form of the 

 fringed arms, and the manner in which they are 

 folded. 



Authorities. For structure, I have depended 

 chiefly on Professor Owen's " Memoir on the Ana- 

 tomy of the Brachiopoda," and on Mr. S. P. Wood- 

 ward's " Manual of the Mollusca ;" for the British 

 species, Messrs. Forbes and Hanley are my au- 

 thority. 



BRACHIOPODA. 



Molluscous animals enveloped in a shell of two 

 valves, of which one is commonly perforated, attached 

 to extraneous substances by a stalk passing through 

 the perforation ; valves applied, the one to the 

 back, the other to the belly; mantle two-leaved, 

 performing respiration, permeated by blood-vessels, 

 and fringed with stiff, straight, horny bristles ; no 

 siphons ; no head ; mouth seated between two long, 



