BRACHIOPODA. 



273 



of Cmtronella 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. 



Fio. 189. Trigtria Chterangeri, de Verneall. 

 The interior of the brachial valve; showing the perforated hinge-plate and the muscular scars. 



(CEhlert.) 



(Ehlert draws attention to the fact that Bayle, in 1875,* applied the name 

 Trigeria to two lower Devonian species, the first, the Terebratula Adrieni, de 

 Verneuil, which was already the type of the genus Retzia, King; the second, 

 Terebratula 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. Qi^HLERx'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 Rensselaria 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 France, Atlas, pi. xiii, figs. 5-12. 

 t Proceedings of the Portland Society of Natural History, vol. i, p. 115, plate, fig. 12. 1862. 

 X For the opportnnity of examining the original specimens of the species we are indebted to Professor 

 B. K. Embrsox, of Amherst College. 



