694 THE ANIMAL KINGDOM. 



less distinctly into lamellae between which are delicate organic membranes. 

 The axes of the prisms are oblique to the surface of the valves. It is rare 

 for the systems of prisms to cross one another or to fuse. A second pris- 

 matic layer may be found in old specimens internal to the first. The 

 substance of the valves is sometimes perforated, but not in Rhynchonellidae^ 

 by vertical canals occasionally branched, which widen at their outer extre- 

 mities beneath the cuticula, e. g. in Terebratula, Tcrcbratella, Waldhcimia^ 

 Spirifer. The canals in question contain hollow or solid processes (van 

 Bemmelen) of the mantle a . The superficial contour lines parallel to the 

 margins of the valves probably represent periods of little or no growth. 

 The calcareous matter is in the form of Calcite except in Lingula, where 

 it consists chiefly of Calcium Phosphate. 



The body of the Brachiopod lies at the base or peduncular end 

 of the shell, more on the side of the dorsal valve than of the ventral, 

 a position most marked in Testicar dines. Two ' mantle ' folds, one dorsal, 

 the other ventral, line the corresponding valves. And the body is as 

 a rule continued posteriorly into a peduncle, usually short, but in the 

 Lingulidae of considerable length, which is attached at its apex to some 

 foreign object. The arms, from which the class obtains its name, have 

 their simplest form in Argiope Kowakwskii among Testicar dines. In 

 this animal the part of the body affixed to the dorsal valve carries a horse- 

 shoe-shaped disc or lophophore, the two arms of the horseshoe being 

 turned towards the free margin of the dorsal valve. The lophophore 

 carries a single and continuous peripheral row of tubular cirri to the inner 

 side of which is a ' brachial' groove bounded on its inner side by a promi- 

 nent fold or lip. The mouth lies in the brachial groove at the centre 

 of the convexity of the horseshoe, therefore within the area inclosed by 

 the lophophore. In A. decollata, as in Thecidiinn^ the lophophore forms 

 four prominent processes instead of two, all turned, however, towards the 

 free margin of the valve. The lophophore of the Terebratulidae is also 

 horseshoe-shaped, but from the centre of the concavity of the horseshoe 

 a process of the lophophoral area extends towards the free margin of the 

 valve, is of great extent, and the edges of its apex are disposed in folds. 

 The cirri, groove and lip follow the edges of the disc and process as in 

 Argiope, and the mouth has the same relation to the groove and the 

 convexity of the horseshoe. The cirri are, however, very numerous, and 

 are arranged either in zigzag or in double file. The disposition of parts is 

 somewhat different in the E car dines, and in the Rhynchonellidae among 

 Testicar dines. The lophophore takes the shape of two long processes or 

 arms which are coiled into a spiral of variable but sometimes of very 



1 The significance of the small globular bodies which occur beneath the cuticle and in the 

 horny layers of the shell of Lingula, and in the processes of the mantle contained within the canals 

 of the shell in 7"esticardines, is not known. Shipley considers them to be blood-corpuscles. 



