76 Br. J. Allan Thomson — Brachiopod Morphology . 



whether dental plates are present or not. A peculiar feature in this 

 species is the divided hinge-plate. It has points of resemblance to 

 some Magaselloid stocks, but does not agree with any known to 

 me. In any case this species cannot find a place in Terehratella or 

 JDallinella. Among fossil genera referred to the Dallininse which 

 show ventral uniplication are Aulacothyris, Trigonosemus, Orthotoma, 

 and Camerothyris, while Antipty china is ventrally biplicate. It is 

 open to question, however, whether these fossil genera really belong- 

 to the Dallininse or to the Magellaninse until the mode of development 

 of their loop is kuown. 



Finally, there are amongst Recent shells ascribed to the Dallininse 

 some which show anterior retardation of the Cincta type. Of these 

 the best example is Terebratula hlanfordi, Dunker, which was 

 described and figured by Davidson as a Terehratella, but was later 

 referred to Laqueus by Dall l on account of its loop characters. This 

 species has a well-marked mesial sinus on each valve and an excavate 

 front, and the same characters are possessed in a lesser degree by 

 Laqueus rubelhis (Sow.) and L. Jeffrey &i (Dall). 2 Of the remaining 

 species ascribed to Laqueus, L. pictus is non-plicate and apparently in 

 the lenticular stage, though there is a tendency towards a straight 

 front, but L. californicus, which is the type of the genus, occupied an 

 anomalous position, for according to Davidson's figures and descriptions 

 it shows the beginnings of ventral uniplication. It appears as if in 

 this case a stock in the lenticular stage were evolving in two 

 directions, giving rise on the one hand to species with ventral 

 uniplication and on the other to species with Cincta retardation. As 

 the process has not gone very far, it seems hardly necessary to 

 separate the Cincta-like forms under a new genus at present. 



Among fossil genera ascribed to the Dallininse which show anterior 

 retardation of the Cincta type are Cincta, Microthyris, Zeilleria, 

 Trigonella, and Trigonellina. 



As in the case of the Terebratulinae, then, we have in the Dallininae 

 genera belonging to each of the three series of folding. It is not 

 suggested that Laqueus hlanfordi is necessarily more nearly related to 

 Cincta than to Ballina or Ilacandrevia. A great deal more must be 

 learned before we are in a position to know the relationship of the 

 various members of the Dallininae to one another, and in this connexion 

 a study of the beak characters, hinge-plate, and cardinal process may 

 be of considerable service. 3 



The simplicity of types of folding in the Magellaninse and the 

 complexity in the Dallininae at least suggest that these two sub- 

 families are not of equal taxonomic value. 



1 Proc.U.S. Nat. Mus., vol. xvii, pp. 724-6, 1895. 



2 Originally described by Dall as Frenula jeffreysi, and later by Davidson as 

 Laqueus calif ornicus, var. vancouveriensis. See Dall, loe. cit. 



3 These characters are proving of considerable aid in separating different 

 stocks of the Magellaninse among New Zealand Tertiary shells which have 

 arrived independently at Magellamform loops. 



