Tol. 63.I ME. S. S. BUCKMAN ON BRACHIOPOD MOKPHOLOGT. 339 



It may be of interest now to trace the developments which could 

 arise from a smooth Cincta on the one hand, and to compare them 

 with those which produce the costate Eudesia on the other ; for, 

 while the smooth Cincta is low down in the one line of development, 

 the costate Eudesia is high up in the other. 



The first phase to be dealt with in this connexion may be called 

 the lenticular stage. The shell is smooth, and the rounded 

 anterior margin gives no evidence of developing either a frontal 

 fold or a frontal truncation ; it could develop in either direction. 

 Cincta orhicularis (Zieten) may be placed as representative of this 

 stage. That in old age it might, like its congeners, develop 

 truncation does not affect the argument. In the stage as figured 

 by Zieten, it stands as a type of a lenticular shell able to develop 

 in various directions. 



The next phase may be called the Cincta-st&ge, whereof Cincta 

 pemummus, sp. nov. 1 may be the representative. In this species 

 the front margin is rounded in youth, truncate in adolescence, 

 incipiently excavate and bilobate in adult, as the growth-lines on 

 the specimen show. The incipiently excavate anterior margin makes 

 the shell appear as if it had been bound by a ligature from the beak 

 over the front. 



The Cincta-st&ge may develop in two directions : out of broad 

 forms would come the quadrifid stage (example Zeilleria quadri- 

 jida, Val.) ; out of narrow forms, the cornute stage (example 

 Z. comuta, Sow.). The former is sufficient for consideration now. 



In the quadrifid stage there is excavation or retardation, not only 

 of the front margin, but of the margin between front and sides. 

 This produces three excavate areas ; and there is quadricarination and 

 quadrilobation, the carinaB running about a third to a half up the 

 valves. 



In placing certain species of Zeilleria after species of Cincta it is 

 not intended to suggest that those species are the actual descendants 

 of Cincta. There are differences about the beak-area and the foramen 

 in Zeilleria and Cincta which rather forbid the connexion : these 

 Zeillerice are more probably derived from morphic equivalents of 

 Cincta. It is evident, however, that forms in the quadrifid stage are 

 in a higher degree of development, so far as their test is concerned, 

 than forms in the Cincta-st&ge ; and that, to arrive at the quadrifid 

 stage, they have passed through a Cincta and a lenticular stage. 



Among the Athyrids of the Spanish Devonian are species showing 

 the quadrifid merging into the next developmental stage — for 

 instance, Athyris Ezquerra (Verneuil & d'Archiac) and A. Collettii 

 (Yern.). 



This next developmental stage may be called the quadri- 

 carinate, or trigonellid stage : in it there is complete quadri- 

 carination extending the full length of the valves, prior stages having 

 disappeared by tachygenesis. The Jurassic example of this stage 

 is the shell from the White Jura called by Quenstedt Terebratula 



1 See Appendix, p. 342. 



