BRACHIOPODA. 
273 
of Centronella glans-fagea, though having the anterior plate much smaller. Cen- 
tronella Guerangeri is known to possess a perforated hinge-plate, though in the 
other species this plate appears to have been divided. 
Fig. 189. Trigeria Guerangeri, cle Verneuil. 
The interior of the brachial valve; showing the perforated hinge-plate and the muscular scars. 
(OilHLER’r.) 
(Ehlert draws attention to the fact that Bayle, in 1875,"* applied the narcie 
Trigeria to two lower Devonian species, the first,N the Terebraiula Adrieni, de 
Verneuil, which was already the type of the genus Retzia, King; the second, 
Terebraiula Guerangeri. This name, unfortunately, was not defined, but as a 
designation is required for these plicated centronellids, it is now proposed to 
make use of the term introduced by this French author, basing its value upon 
his second species. Trigeria is represented in the Oriskany sandstone at 
Cumberland, Maryland, by a species very similar to T. Gaudryi; indeed, upon 
careful comparison with Dr. OEhlert’s description and figures there seems no 
good basis of distinction between the two forms, and the American fossil will 
be thus referred awaiting further evidence. It is quite probable that the species 
described by Billings as Rensselceria Portlandica,-\ from the Lower Helderberg 
fauna of Square Lake, Maine, is another representative of the same type of 
structure.^ 
* Explication de la Carte Geologique de Fi-ance, Atlas, pi. xiii, figs. 5-12. 
t Proceedings of the Portland Society of Natural History, vol. i, p. 115, xilate, fig. 12. 1862. 
J For the opportunity of examining the original specimens of the species we are indebted to Professor 
B. K. Emerson, of Amherst College. 
