46 
PALAEONTOLOGY OF NEW YORK. 
Trimerella, linked to typical specimens of the genus by species like T. Billingsi, 
Dali, in which the platform-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 central 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 
Palaeozoic 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 
be 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 Rhinobolus 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. 
OBSERVATIONS ON THE DEVELOPMENT AND FUNCTION OF THE PLATFORM 
IN THE INARTICULATE BRACHIOPODA. 
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 Rhinobolus it constitutes the principal diagnostic character of the 
Family Tjumebellid^e 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 
