CLASSIFICATION OF THE BRACHIOPODA. 113 



able to admit the conclusions arrived at by the learned Professor ; and, on the contrary, 

 firmly believe that the four above-mentioned genera are not only intimately related, but 

 even lead me to doubt whether we are authorised in admitting as many as four genera.' 

 None of the characters above described are found among the Strophomenida, where both 

 the muscular and vascular system is essentially different ; and the only similarity appears 

 to consist in the presence in some of the PRODUCTiDiE, of an area and pseudo-deltidium. 

 The character of the area is essentially similar in Chonetes, Strophalosia, and Anlosteges, 

 still the first two have a distinctly articulated hinge, while the last {Atdosteffes), whose area 

 and deltidium are far more developed than in the other two, is unarticulated, and thus 

 intimately connect Strophalosia with Productus. 



Genus — Chonetes, Fischer, 1837. 



Type—C. SARCiNULATA, Schl., sp. Int., PI. VIII, figs, 198—202. 



Pectinites, Lister. 



Pectuncultjs, Volkmann. 



Pectunculites, Walch. 



Pecten, Ure. 



Hysterolites et Terebratulites, sp., F. Schloth. 



Productus, sp., J. de Sow., F. Buck. 



Orthis 1 (part), Dalman, Goldfuss, and of many Authors. 



Lept^ena (part), F. Buck, J. Sow., M'Coy, &c. 



Spirifera (part), Phillips. 



Chonetes, Fischer, De Koninck, Be Ferneuil, and the generaUty of Authors. 



Strophomena, sp., J. Hall, &c. 



Delthyris, sp., Fahrenkohl. 



Shell inequivalve, compressed, transversely semicircular, with a straight hinge line, com- 

 monly as long as the width of the shell, or prolonged in the shape of auricular expansions ; 

 dental valve convex, depressed towards the cardinal edge ; socket valve always concave, 

 following the curves of the other ; area distinct, almost equal in both valves, or larger and 

 more produced in the dental one ; the upper edge of the area in the larger valve is acute, 

 and provided with a row of delicate spinose hollow tubes, varying in number in different 

 species, and becoming gradually longer as they recede from the extremity of the beak, 

 diverging obliquely from the hinge line ; fissure covered by a pseudo-deltidium. In the 

 socket valve the opening is entirely filled up by a projecting bifid or trifid cardinal 

 process ; surface ornamented with minute, longitudinal, dichotomised, or intercalated striae, 

 rarely largely plaited, but transversely marked by concentric lines of growth. 



Internally, the valves articulate by means of teeth placed at the sides of the fissure of the 



^ M. de Koninck admits only two genera in the family: viz., 1, Chonetes; 2, Productus, which last 

 includes Strophalosia, King, and Aulosteges, Helm. 



15 



