13 

 WEDNESDAY, DECEMBER 13th, 1893. 



THE EVOLUTION OF THE BRACHIOPODA. 



BY 



MISS AGNES CRANE. 



Brachiopoda, said Miss Crane, were the " arm footed " 

 shell fish, a little lower than the oyster, and one of the main 

 moUuscan roots of the tree of animal life. It would, she remarked 

 in passing, be well if all those who discuss the doctrine of 

 Evolution were to study the life history of any one class of 

 animals and trace the fossil ancestry of its present representatives, 

 to investigate not only the inter-relations of such a group of 

 organisms among themselves, but with those of the class below 

 and the one above them, so as to realise better the true nature 

 of collateral descent and what is meant by a common origin. 



An epitome of the life history of the Brachiopoda was then 

 given. It showed their universal distribution in existing oceans 

 from shallow water down to 2,900 fathoms, the enormous depth 

 of three miles and a quarter, in the Atlantic Ocean. Their range 

 in time was no less extended, for the shells occur fossil in all 

 marine deposits, ranging from the primordial to the quarternary 

 genera, and species were most abundant " of old time." Two- 

 thirds of the whole number appeared in the seas of the palaeozoic 

 epoch. The differences in the structure of the shells and animala 

 belonging respectively to the two sub-classes of hinged and 

 hingeless forms were described and illustrated. Of the thousands 

 of species which existed " afore time," about 129 now survive, 

 referable to 22 genera and seven families. According to the 

 returns of the last census of the Brachiopoda taken and tabulated 

 this year by Mr. Charles Schuchert, of Washington, 277 genera 

 are now known acd described, referred to 47 family groups, of 

 which no less than forty have become extinct, whilst seven are 

 represented in existing oceans. The Brachiopoda have been 

 recently classed by Beecher, of Yale Museum, in four orders, 

 based on the nature of the pedicle passage and the stages of shell 

 growth. The evolution in time of these orders was shown by a 

 large coloured diagram prepared for the occasion. It indicated 

 their common origin and the divergence on either side of the 



