Thomson. — Brachiopod Genera. 393 



It will clear the ground to indicate first the validity of the genera 

 Neothyris Douville and Pachymagas Ihering. Douville* separated Neothyris 

 (genotype, Terebratula lenticularis Desh.) from Waldheimiaf (genotype, 

 Terebratula australis Quoy and Gaimard= T . flavescens Lamarck) on grounds 

 of different types of folding. The former he placed among the Cinctae, 

 stating that the valves are without folds and the commissure almost plane. 

 It is true that the valves are almost without folds, but the anterior com- 

 missure exhibits a slight but distinct anterior depression, a feature more 

 stronglv marked in related species, and due to incipient ventral uniplication. 

 The folding, therefore, places this species among the Nucleatae, and not 

 among the Cinctae. In the other species, WaMheimia flavescens (Magellania), 

 Douville distinguished primary and secondary folds, and placed the species, 

 on account of its primary folds, in the group of Coarctatae — i.e., antiplicate 

 or ventrally biplicate. In this respect Douville was, I believe, justified. J 

 The triplication is certainly slight in M.flavescens, but it is quite well marked 

 in certain Australian Tertiary forms, such as M . grandis, M. garribaldiana, 

 and M. divaricata. Nevertheless, it is not in itself a character of generic 

 importance in this case. The whole of the Magellaninae, if folded at all, 

 show a dominant ventral uniplication, § and the feeble ventral biplication is 

 only a slight modification of this, and has arisen independently in more 

 than one evolutionary stock. Actually it appears to be confined to Australian 

 forms, but it is not yet certain that they will all come under Magellania 

 s. str. 



There is, however, another important difference between M. lenticularis 

 and M . flavescens, and it is precisely that used by Ihering in 1903 to dis- 

 tinguish Pachymagas from Terebratella — viz., the difference in the hinge- 

 plate and cardinal process. " Comparee avec T. dorsata, le plateau cardinal, 

 comme aussi ses annexes et le septum, sont extremement grossis et ces caracteres 

 servent pour etablir un sous-genre, pour lequelje propose le nom de Pachymagas. 

 L'espece typique est T. tehuelca et il jaut placer dans le mime sous-genre, 

 T. gigantea Ortm. et venter Ih. Toutes ces especes sont eteintes et restreintes 

 aux depots tertiares de la Patagonie ; toutes ont la coquille lisse, tandis que 

 dans Terebratella s. str., le processus cardinal, les crura et le septum sont 

 minces, plus ou moins lamellaires et la surface externe des valves est munie 

 de larges cotes rayonnantes."\\ 



Before discussing the cardinal process and other hinge parts it will be 

 convenient to dispose of the accessory character of multicostation, which 

 is shared both by M.flavescens and T. dorsata, the genotypes of Magellania 

 and Terebratella respectively. It is confined, among the higher genera of 



* Bull. Soc. Geol. Fr., t. 7 (1879), pp. 273-75. 



t Waldheimia was found to be preoccupied, and the name was changed to Magellania 

 by Bayle in 1880. 



X Buckman apparently did not recognize the biplication. He says (Quart. Journ. 

 Geol. Soc, vol. 63 (1907),' p. 342), "Hall and Clarke speak of Magellania numismalis, 

 the present Cincta ; but M. flavescens has not come through a Cincta stage, and shows 

 no sign of anterior retardation of the Cincta type. What it does show a little indication 

 of is a uniplicate stage, but reversed as compared with Terebratula whitakeri — that is, 

 it is ventrally, not dorsally, plicate." 



§ With the exception only of Magasella vercoi Blockman, which shows slight dorsal 

 uniplication, and of M. adamsi Davidson, a species whose position in the Magellaninae 

 is not unequivocal. It is probably not an adult shell, and may be the young of some 

 member of the Dallininae. 



|| H. von Ihering, " Les Brachiopodes Tertiares de Pptagonie," Ann. Mus. Nac. 

 Buenos Aires, torn. 9 (1903), p. 332. 



