BRACHIOPODA. 
271 
plecia?) apiculata and A. (T. ?) incerta, the cardinal area is remarkably high and 
erect, and the median fold is on the pedicle-valve instead of on the brachial 
valve, as in the typical species. Should these prove genuine Triplecias, the 
reversal of the relative convexity of the valves will be an occurrence similar 
to that observed in the species of Mimulus. The species Produda (T. ?) monili- 
fera appears to be a normally symmetrical, or slightly unsymmetrical (see plate 
xxv, fig. 5) Streptis, and the T. ? Grayce, a form with an erect cardinal area 
and a strongly radiate surface ornamentation. In one of these radiated species, 
the Orthis spiriferoides, McCoy, from the Upper Llandeilo and Caradoc, the ex¬ 
istence of the peculiar articulating apophyses of Triplecia has been demon¬ 
strated. (See Plate XI a, figs. 10,11.) This species was referred to Triplecia 
with doubt by Mr. Davidson, but the certainty of its being congeneric with 
T. extans in these important features, opens the genus for the present to the 
reception of similar radiated shells. Another excellent representative of this 
type of structure is the Orthisina cava, Barrande,* from the Etage D 2 . 
Leaving out of consideration the Camarella calcifera, Billings, and the Triple¬ 
cia primordialis, Whitfield, the earliest known representative of this genus in 
American faunas, appears to have been such a radiated form, T. radiata, Whit¬ 
field, from the Calciferous fauna at Beekmantown, N. Y. In the fauna of the 
Trenton group are T. extans, T. cuspidata and T. nucleus; the only other member 
of the genus known in this country being the T. Ortoni, from the Clinton fauna 
of Ohio. 
Systeme Silurien da Centre de la Boheme, vol. v, pi. 59, figs, iv, 1-7. 
