110 Miss Agnes Crane — Evolution of the BracJiiopoda. 



and consequent displacement of the organ usually called " the liver" 

 (stomacal gland of Joubin) (47) affected the position of the muscles, 

 which grew strong in proportion as the shells grew massive. The 

 combination of increased muscular energy and resulting augmented 

 secretion of shelly substance or " stereom " in the area of muscular 

 attachment caused the formation of a solid plate, which has been 

 gradually changed into a more or less vaulted platform. The 

 evolution proceeded on two distinct lines. One deviated from 

 Lingula, travelled via Lingulops and Lingulnsma, with muscular scars 

 excavated or sunken as in Lingula. The other diverged from 

 Primordial Obolus through Elkania to Dinobolus with elevated 

 muscular attachments. Both lines culminated in the Trimerellidaa 

 before the close of the Silurian period in Canada, the United States, 

 and Gotland, Sweden (32). 



Similar instances of development on parallel lines can be traced 

 in the longer known families of the Ehynchonellidge and the Tere- 

 bratellidge (King emend Beecher). It has been clearly demonstrated 

 by Deslongchamps (34), Buckmanand Walker (13), that the "acute." 

 the four-cornered, the " spinose," and some other Ehynchonelloid 

 groups of the Jurassic period — I now quote verbatim — " carry on as 

 they ascend each their own course of development side by side." 

 The earliest forms of the intermediate Proto-rhynchoids are found 

 in the Lower Silurian. 



The results of the various researches into the development of 

 the Terebratuloids have been so recently summarized by myself^ 

 in this Magazine and elsewhere, that it is not necessary to go into 

 details of what may truly be regarded as a test case of the evolution 

 of the Brachiopoda. 



Friele (36), Dall (24), Deslongchamps (28, 29), and Beecher (7) 

 have traced the specific development of the northern members of the 

 long-looped Terebratellidaa, and those of the southern oceans have 

 been the subject of detailed comparison and research by Dr. P. 

 Fischer, and those excellent French Zoologists Daniel and Pauline 

 (Ehlert (59), whose collaboration has been so fruitful in research, 

 and is full of promise for the future. 



It is with pleasure I refer to Madame Pauline CEhlert as an 

 earnest co-worker with her distinguished husband, and, so far as 

 I am aware, the only other member of my sex who is actively 

 interested in the study of the recent and fossil Brachiopoda (59, 60, 

 61, 62, 63). 



So far as the Terebratelloid branch is concerned the combined 

 results of all investigations reveal two lines of generic evolution. 

 One travelled by the northern and the other by the southern 

 species of the family. In each the earlier stages, gwyniform and 

 cistelliform, are identical, and indicate descent from a common 

 Megathyrid source (7, 8). The northern forms pass successively on 

 through the platidiform, ismeniform, miihlfeldtiform, terebratelli- 

 form, and culminate in the dalliniform phase represented in boreal 



1 Geol. Mag. Dec. 3, 1893, p. 321. Natural Science, vol. ii. No. 11, Jan. 1893, 

 pp. 46-52. 



