356 ZOOLOGY. 



BRACHIOPODS. 



RANGE IN DEPTH OF LIVING BRACHIOPODS. 



Mr. Thomas Davidson has examiued the collection of Brachiopods 

 secured by n. M. S. Challenger, and in connection therewith has enu- 

 merated all the existing- species of the class.* It was thought that 

 many novel forms would be obtained b^' the dredge from the dei)ths of 

 the sea, but this anticipation has not been realized. Very few new 

 species were found during the voyage of the Challenger, and noue rep- 

 resenting genera that had not before been known from representatives 

 living in waters of less depth. One hundred and thirty-six living spe- 

 cies or sub-species are recognized by Mr. Davidson, 125 so-termed "spe- 

 cies," and 11 "named varieties"; but, it is added by Mr. Davidson, the 

 number " will certainly have to be hereafter reduced." Not more than 

 31 species were obtained by the Challenger expedition, and out of 3G1 

 stations at which dredgings were made Brachiopoda " were brought up 

 38 or 39 times onlj ." The circumstances respecting the discovery of 107 

 of the recognized named forms have been ascertaiued, while "nothing is 

 known respecting the ranges of depths of some 25 or 2G so-called spe- 

 cies." Of the 107 species (or named varieties) some 57, or about half 

 the known species, were dredged at a depth of under 100 fathoms ; 20 to 

 25 at low- water mark, or from 5 to 10 fathoms ; and the remainder at 

 about 50 or 60 fathoms," or, to be more delinite, the status of our infor- 

 mation may be given in the following table: 



Species. 

 From shore to 500 fiithoms some 98 



or named varieties ; 12 of these range uji to 100 fathoms or less. 

 From 501 to 1,000 fathoms 16 



Of these only one, Disceria Atlantica, would range from 690 to 

 2,400 fathoms. 

 From 1,001 to 1,500 fathoms 6 



Of these Terebratuki icyviUii ranges from 1,035 to 2,000 fathoms, 

 the greatest depth at which any species has been found. 



From 1,501 to 2,000 fathoms 4 



From 2,001 to 2,900 3 



Mr. Davidson concludes that " these facts indicate that the greater 

 bulk of known species live at comparatively small or moderate depths, 

 few in depths ranging up to 500 fathoms, and that Brachiopoda are 

 specifically rare at depths varying from 500 to 2,900 fathoms. 



It is to be regretted that Mr. Davidson still clings to the names Clis- 

 tenterata and Tretenterata when exactly the same groups with the same 

 limits, and the same essential diagnoses, had received each several names 

 long before. If any objections are urged against those previous names, 



* Davidson (Thomas). Report ou the Scientific Results of the Voyage of H. M. S. 

 Challeuger, dviriug the years 1S73-'7G. Zoology, vol. i, part 1. Report on the Bi'ach- 

 iopods. Printed by order of Her^ Majesty's Government, Londonj 1880. 



