342 



appendages called deltidia^ wliich are in some species united together 

 in the middle, iu which case the perforation is rendered entire ; 

 when they are separated it is incomplete : these deltidia are of an 

 elongated form and continue from the anterior margin of the 

 cardinal area to the apex in those species (T. psittacea and 

 T. nigricans) that have a pointed beak. It is also to be remarked 

 that these species are not punctated on the surface as aU other 

 species are. 



Terehratnia was formerly placed among his Anomia by Linne ; 

 it is however very easily distinguished from the legitimate Anomia, 

 by its regularity, its produced beak, its being attached by a fibrous 

 peduncle and by its internal appendage. The recent species of 

 the genus are found in all climates, and they are for the most part 

 very abundant in all localities where they occur. 



We have never been able to meet with T. roiundata of Lam. 

 represented in Encycl. meth. t. 239. f. 5. 



DESCRIPTIONS. 



Impunctata. 



1. Terebratula psittacea (pi. Ixxi. f. 78, 79, 80.) Lam. 



Testa subglobosa, postice acuminata, tenui, nigricante, valvis 

 inajqualibus, radiatim concinne striatis, linea marginali ex umbones 

 declivi, demiim ascendente et antice valde sinuata ; valva dorsali 

 postice acuta, recurva, antice deflexa, sulco mediano lato, indistincto, 

 foramine trigonali, baud integro ; area cardinali incouspicua, ro- 

 tundata, deltidiis angustis, ad lateres foramiuis coalescentibus ; 

 valva ventrali ventricosa, antice latiori, carina mediana inconspicua, 

 ad marginem anticum solummodo distincta ; dentibiis cardinalibus 

 internis ex umbonem porrectis recurvis duobus ad utrumque latus 

 uno : margine valvarum integerrimo. 



From Labrador, where it is found in abundance in the mud on 

 the shore at low water : dredged alive at MelviUe Island by Lieut. 

 Griffith. 



2. Terebratula nigricans (pi. Ixxi. f. 81, 82.) nohis. 



Testa antice rotundata, postice acuminata, tenuiuscula, nigricante, 

 valvis insequalibus, radiatim costatis, costis roiundatis, linea margi- 

 nali rectiuscula; valva dorsali subtrigona, depressiuscula ; antice 

 rotundata, lateribus posticis declivibus, foramine magno, hand 

 integro, quadrato ; area cardinali magna, planiuscula, lateribus 



