Miss Agnes Crane — Evolution of the Brachiopoda. Ill 



oceans by Waldheimia septigera and Macandrevia cranium. The 

 austral species diverge, after assuming the cistella stage, through 

 a bouchardiform, mergerliniform, magasiform, magaselliform, tere- 

 bratelliform, and magellanit'orm phase, of which the fine Falkland 

 species Magellania (W.) venosa, Sol., is the type of final evolution 

 (59. 61). 



These forms or phases, transitional and successive, in the living 

 species often represent adult stages known to be permanently 

 stereotyped as charactei'istic genera in the fossiliferous deposits of 

 the Tertiary, Cretaceous, and Jurassic formations. In the Devonian 

 epoch the Terebratelloid branches become merged in the main stem. 

 The well-marked Devonian genus Tropidoleptus ^ is, according to 

 Hall, a true platidiform type, and one of the oldest known repre- 

 sentatives of the Terebratellidge, while Cryptonella, also of Devonian 

 age, is likewise regarded by him as a direct ancestor of the Magellanian 

 stock ( Waldheimia). There is evidence that both branches originated 

 in the earlier •' stropho-orthoid " stock of the protrematous order. 

 The annectent genus Amphigenia, on the other hand, approximates 

 both to the Rhynchonelloid branch and the main Terebratuloid stem, 

 as represented by the Lower Devonian Rensseloeria, "half Penta- 

 meroid, half Centronelloid," and others of the ceutronelliform type. 

 Its appearance in the Upper Helderberg series of tlie Lower 

 Devonian somewhat antedates that of Rensseloeria. Amphigenia is 

 punctate and unites the muscular scars of the Terebratuloid with 

 a spondylium and the brachial processes of a Rhynchonelloid, and 

 thus connects the Pentameroids with the Terebratuloids, Among 

 the earlier orthidian and pentamerine stocks the Proto-rhynchoids 

 also originated in Lower Silurian times, culminating in the persistent 

 Ehynchonelloid stem, still represented by the more modern offshoots 

 Hemitliyris and Acauthothyris of the Telotrematous order, so prolific 

 near its source in the comparatively short ranging spire-bearing 

 genera, of which the last representatives died out in the Triassic 

 oceans. 



But it is impossible, even in the generous space limits permitted, 

 to go farther into details of descent with modification among the 

 Brachiopoda. We have seen, as we search together the records of 

 the ancient fossiliferous rocks, how the confines of the classes merge 

 into one another, that orders converge and certain genera pass 

 almost insensibly the one into the other.^ Our knowledge has, 

 indeed, advanced with giant strides of late, thanks to the critical 

 and searching investigations of the numerous able scientists of 

 diverse nationalities interested in this group of organisms, and to 

 those of America, France, and Germany in particular. I feel sure 

 that there is awaiting us in the not far distant future a complete 

 demonstration of the evolution of the Brachiopoda. 



^ This genus has no deltidiiim on the brachial valve. 



* " Even among the generic groups there is so often an almost intangible transition 

 from one to another that the employmeut of distinctive terms seems at times quite 

 perfunctory ; but with the increase of such difficulties the nearer our classification 

 may be regarded as approaching the true method of development." — Vide -p. 908, 

 Hall and Clarke's "Handbook of the Erachiopoda," Part II. Albany, 1895. 



