46 PALEONTOLOGY OF NEW YORK. 



Trimerella, linked to typical specimens of the genus by species like T. Billingsf, 

 Dall, in wliich the platfonn-vaults are quite short, does not seem in accord with 

 the persistent abbreviation of the platform and the entire absence of platform- 

 vaults and umbonal cavities. We can, indeed, find an analogy to Trimerella 

 solely in the development of the deltidium of the pedicle-valve, while the 

 similarity to Dinobolus in the structure of the platform is more apparent, though 

 still remote. In the features of the brachial valve, however, the agreement 

 with MoNOMERELLA is by no means remote, as is seen in the marked difference 

 of the centnil and lateral scars Mr. Davidson afterward abandoned his view 

 expressed above, in regard to the relations of these forms, as we learn by an 

 extract from a letter to Mr. Whiteaves, quoted by the latter at page 8 of the 

 PaliBozoic Fossils, vol. iii, pt. 1 : 



" Although with much uncertainty this shell was placed, by Professor King 

 and myself, in the genus Trimerella, it is not a true Trimerella, and should 

 Ije removed from that genus. It is more closely allied to Monomerella, and 

 perhaps it would be better to retain Professor Hall's generic name of Rhynobo- 

 Lus for its reception." 



In addition to the features already mentioned, the species of Rhinobolos show, 

 on both brachial and pedicle-valves, the broad terminal scars at the extremity 

 of the sharply developed crescent, and, in the pedicle-valves, the umbo-lateral 

 scars ; the great trunks of the pallial sinuses are faint, though discernible. 



OBSKRVATIONH OX THE DEVELOPMENT AND FUNCTION OF THE PLATFORM 

 IN THE INARTICULATE BRACIIIOPODA. 



The .specialized post-median testaceous deposit which has been termed the 

 "platform" by Messrs. Davidson and King, occurs among brachiopoda only in 

 the genera Lakhmina, Lingulops, Lingulasma, Dinobolus, Trimerella, Monomer- 

 ella and lliirxoBOLUs; it constitutes the principal diagnostic character of the 

 Famihj Thimehelltd^ of those authors, and in so far as any of these genera pos- 

 sesses this feature, so far, at least, is it a Trimerellid. In its chronogenesis it 



