THE BRITISH FOSSIL BRACHIOPODA. 289 



and no good would be attained by altering them. At page 851 of his admirable memoir on 

 the organisation of the Brachiopoda, Hancock says : — " The valves of the Brachiopoda are 

 undoubtedly related anatomically, as stated in the text, although, perhaps, they aught both 

 to be considered dorsal as well as those of the Lamellibranchs, as has been pointed out 

 by Prof. Huxley. If this view be correct, the only difference in the arrangement of the 

 valves of the two classes will be that, while in the latter they are united along the dorsal 

 ridge, they are articulated across the back of the Brachiopod." The valves have also 

 been sometimes distinguished by the names of dental and socket valves, but this would 

 not hold good in those species that are unprovided with teeth and sockets. Dr. Jeffreys 

 terms them "upper'' and "lower," and in the fourth page of the second volume of his 

 excellent work on " British Conchology " he says : " When the Terebratula is attached by 

 its peduncle the perforated valve is the uppermost, the back of the Terebratula is really 

 that part which lies between the arms and mouth, and is close to the apex or point of 

 attachment. Instead, therefore, of calling the valves "ventral" and "dorsal" it would 

 seem more correct to describe them as "upper" and "lower" the larger and deeper 

 valve being perforate and uppermost, and the smaller and shallower valve being imper- 

 forate and the lowermost." Prof. King makes use of the names '■'large valve" and 

 " small valve " in his descriptions. 



Prof. H. W. Caldwell, in his preliminary note on the structures and affinities of 

 Phoronis and the Brachiopoda, 1 says that both valves are ventral ; and in a letter to me he 

 adds, " The valves of the Brachiopoda, after my views, lie in the regions of the body sur- 

 face corresponding to the anterior and posterior ventral of other forms. Thus the larger 

 valve of Testicardines is anterior, the small, flatter ' dorsal ' valve posterior. In Ecardines 

 the smaller valve is homologous with the anterior, the larger with the posterior. In des- 

 cribing them I do not propose to use other terms than these, viz. anterior and posterior 

 shells/' 



The ventral valve is usually the larger, and in many genera, as in the Tereiratulida, 

 has a more or less prominent beak, with a circular foramen at or near to its extremity, 

 partly or entirely margined by one or two plates constituting the "deltidium." In 

 other forms there exists a triangular fissure, which either remains open or is partly or 

 entirely arched over by a pseudo-deltidium. In some forms, such as in Cgrtia exporrecta, 

 Strophomena rhomboidalis, and others, a circular foramen exists in the young age at the 

 extremity of the beak or in some part of the arched deltidium and continues open for 

 some time, when it becomes closed or cicatrised in the adult. Through the foramen 

 passes a bundle of muscular fibres by which the animal is attached to marine objects. 

 Some adhered to submarine objects by a larger or smaller portion of the surface or 

 substance of their ventral valves, as in Crania parisiensis, Davidsonia Verneuili, &c, or 

 by long spines which were wound round bodies of attachment as in Prodactus complectens 

 and other species. Lastly, many forms seem never to have been attached at all. 

 1 'Proceedings of the Royal Society,' vol. xxxiv, Nos. 222, pp. 371 — 382, 1882. 



