1893. EVOLUTION OF BRACHIOPODA. 49 



accounts for the wide distribution of the abyssal fauna. During the 

 Pliocene period, the cold currents penetrated into the Mediterranean, 

 which then received a number of hardy boreal species, the remains of 

 which have been preserved in the fossiliferous deposits of Ficcarazzi, 

 in Sicily. The elevation of the sea-bottom at the Straits of Gibraltar 

 checked the inflow of the cooler currents of the ocean depths, with 

 the consequent result of a gradual rise of temperature in the then 

 nearly enclosed sea. The abyssal forms, being unable to accommo- 

 date themselves to the changed conditions, died out in the thermal 

 waters, but their collaterals continued to iiourish and multiply in the 

 favourable and unchanged conditions of the Atlantic Ocean (2). 



These considerations. Dr. Fischer and D.-P. CEhlert maintain, 

 confirm the hypothesis that the distribution of marine species is prin- 

 cipally regulated by the temperature of the waters. Hence it arises 

 that the Mediterranean Sea now possesses a rich surface fauna and 

 a poor abyssal one ; while the Lusitanian province beyond is charac- 

 terised by a poor surface fauna and a deep-water fauna of extra- 

 ordinary richness and vitality. 



The results derived from a careful study of the specimens 

 obtained by the " Romanche" during the French scientific mission to 

 Cape Horn (4) were of a dififerent character, and, while affording some 

 distributional data of interest, which serve to emphasise the great 

 dissimilarity existing between the boreal and the austral brachiopodal 

 fauna, yielded more important evidence concerning the transitional 

 stages of development of the larger southern species of TerebrateUa 

 and Magcllania. ■ These successive stages are shown to be of a more 

 complicated character and to differ somewhat from those undergone 

 by the northern forms as first described by Herman Friele, who based 

 thereon his simple division of the great family of Terebratulidae into 

 two groups of the short loops and the long loops since generally 

 adopted. It is now quite clear that the genus so long known as 

 Waldheimia is a closed type, the ultimate phase of a long line of develop- 

 ment through successive pre-magadiform, magadiform, magaselli- 

 form, and terebratelliform stages culminating in the southern seas in 

 Magellania venosa, M. leniiailaris, and M. grayii. It is remarkable that 

 the species of the Northern Ocean should reach the same goal by a 

 shorter line and somewhat different stages, which CEhlert and Fischer 

 define as centronelliform, ismeniform and terebratelliform, ultimately 

 attaining the Magellanian grade as represented by Wald. septigera and 

 Macandreii'ia crannm (4). 



Davidson's classification of the long-looped species of Waldheimia 

 with the short-looped species of Terebraiula, Liothyris and Tevehratulina, 

 which assume their stable generic loop characters without undergoing 

 any metamorphoses, cannot possibly be longer sustained. It is quite 

 evident that Magellania has absolutely no affinities with the sub-famil}' 

 Terebratulinse, but must be associated with the Terebratellince and 

 should rank above that genus in a natural scheme of classification, as 



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