Thomson. — Brachiopod Genera . 



401 



Nevertheless, its nearness in shape to Magadina is shown by the fact that 

 Tate states that it bears considerable external resemblance to M. cumingi, 

 while Pritchard has placed it as a synonym of M. com/pta* The loop is 

 much more advanced than that of Magadina, however, being an early 

 Terebratelliform stage. Its hinge characters, described below, are quite 

 distinct from those of Terebratella and Pachymagas. Although, from the 



Fig. \3.— Magadinella woodsiana (Tate), River Murray. 

 (After specimens in the Dominion Museum.) 



slight difference in beak characters, Magadinella woodsiana cannot possibly 

 itself be an ancestral form of RJiizothyris, the forerunner of Rhizothyris with 

 Terebratelliform loop may be placed, when it is found, under Magadinella. 



Hinge Characters of the Bouchardia-Rhizothyris Series. 



In Bouchardia the posterior parts of the valves are much thickened, 

 the hinge-teeth of the ventral valve are strongly bifid, while in the dorsal 

 valve the fusion of the parts prevents exact comparison with the socket- 

 ridges, cardinal process, &c, of more advanced genera. The adductor and 

 diductor muscular impressions are situated anteriorly in the ventral valve, 

 and are divided by a low median ridge. In Magadina the valves are still 

 somewhat thickened posteriorly, the hinge-teeth are more strongly bifid 

 than in advanced genera, while the median ridge separating the muscular 

 impressions on the ventral valve is still situated anteriorly. The thickened 

 hinge parts of the dorsal valve consist principally of two socket-ridges, 

 which posteriorly are separate and taper each nearly to a point, projecting 

 considerably behind the umbo, but anteriorly are very solid, and unite with 

 one another in front of the septum. Between them, behind their anterior 

 junction, there is a small but deep hinge-trough, in which a cardinal process 

 lies. In Magadina broivni this process is very small, but in M. eumingi 

 it is large and solid, without sharp angles, and completely fills and obscures 

 the hinge-trough. The septum, high in front, low behind, joins the anterior 

 junction of the socket-ridges without bifurcation. 



In Magadinella the posterior thickening of the valves is greatly reduced, 

 while the muscular impressions of the ventral valve are situated posteriorly 

 as in other advanced genera. The septum is long but low,f so that the 

 loop is probably in an early Terebratelliform stage. The hinge characters, 

 however, still present considerable resemblance to those of Magadina. The 

 socket-ridges are swollen anteriorly, almost uniting in the middle, where 

 they are joined by an unbifurcated septum ; posteriorly they become 

 attenuated, and project considerably behind the umbo. The hinge-trough 



* Proc. Roy. Soc. Vict., n.s., vol. 8 (1896), p. 143. 



t Tate's figure shows a septum moderately high anteriorly, due probably to the 

 youth of the shell figured. 



