30 PALAEONTOLOGY OF NEW YORK. 



in the adjacent beds, and the more recent discovery b}- Dr. Warth, of trilobites 

 in the " Obolus-beds," which have been referred by Waagen to the genera 

 Conocephalites and Oleniis{?), point conclusively to such an age* Never- 

 theless, some of the brachiopod genera show certain details of structure which 

 indicate an important progress from the types exemplified in their nearest 

 primordial allies; for example, the great cardinal process in Neobolus, the 

 hinge-line in Cakdixocrania, and thus, also, in Lakhmina,. the cardinal process 

 in the brachial valve is developed to a greater degree than has been observed 

 among the later Trimerellids, The peculiar modification of the platform in this 

 valvf is also an important character. The advance apparent in the develop- 

 ment of this feature in the brachial valve of Lingulops and Lingulasma, over 

 that of the opposite valve, is here seen in the strongly elevated, though short, 

 deeply enrolled posterior plate. The single species of this genus is quite small, 

 and some of its internal characters are not well understood. 



The ge.nera Trimerella, Dinobolus, Monomerella, and Rhinobolus, show a 

 remarkable uniformity in their broadest characters, which may be expressed 

 by the following anaWsis of the Family Thimerellidji, Davidson and King : 



Shells essentially calcareous, usually thick and heavy. Umbo of the pedicle- 

 valve generally high, solid or hollow ; wlien the latter, double or triple- 

 chambered. Cardinal area well developed ; hinge-line inarticulate or with 

 rudimentary teeth (?) ; supported in the pedicle-valve by a vertical axial 

 wall or buttress. Each valve bears, in its post-median portion, a more or 

 less conspicuously developed platform, which may be solid or hollow ; when 

 the latter, it is double-chambered ; from its anterior end extends a vertical 

 septum, which is usually larger in the brachial, than in the pedicle-valve. A 

 narrow crescentic impression lies just within the hinge-line, terminating 

 within the lateral margins in broad muscular scars. The surface of the plat- 

 I'orm bears three or four pairs of similar scars. The pallial sinuses make a 

 l)road curve over the anterior area of each valve. 



This group has been made the subject of an exhaustive analysis by Drs. 



* See Note dh the Discovery of Tnlobites by Di-. H. Wartb, in the NeoboIus-beJs of the Salt-Rangre ; 

 by the Director, Geological Survey ipf India; Recoi-ds Geol. Surv. India, vol. xxii, pt. S, p. 153. 1889. 



