NARRATIVE OF THE CRUISE. 



131 



,[ The Brachiopoda are a most interesting and important class among the Invertebrata, 

 from the fact that they represent the earliest known forms of life, and have continued to 

 exist under a variety of more or less allied species up to the present time. They appear, 

 however, to be much localised, for although the dredge or trawl had been put down 

 by the Challenger Expedition at about 250 stations, Brachiopoda were brought up 38 

 or 39 times only. 1 Out of about 120 known recent species, 34 only were obtained, 

 and out of this number 27 were dredged at depths varying from 2 to 600 fathoms, and 

 the remaining 7 from 1035 to 2900 fathoms. The investigations carried out by the 

 Challenger Expedition tend to prove that abyssal forms are less localised than those 

 that occur in seas of moderate depth ; but deep-sea species, as far as our present 

 experience goes, are of small size, and specifically few in number. Their shell is 



-m 



Pig. 50. — Terebratula wyvillii, 

 Dav., enlarged. 



Fio. 51. — Terebratulina wyvillii, Dav., natural size. 



Fro. 52. — Discina atlantica, King, 

 enlarged. 



extremely thin, glassy, and semi-transparent, as in Terebratula wyvillii, Terebratula 

 dalli, Waldheimia wyvillii, Waldheimia tenera, Terebratella frielii, Atretia gnomon, 

 Discina atlantica, and one or two others. 



•' The three most interesting species brought home by the Expedition were Tere- 

 bratula wyvillii, Terebratulina wyvillii, and Discina atlantica. 



" Terebratulina wyvillii, Dav., is the largest species of the genus, either recent or fossil, 

 hitherto discovered. One specimen only was dredged, on the 25th March 1873, off 

 Culebra Island, to the northwest of St. Thomas in the West Indies, Station 24, depth 

 390 fathoms. 



" Terebratula wyvillii, Dav., is one of the most remarkable of the series of small abyssal 



1 In the opinion of the Naturalists of the Expedition this may, to some extent, be due to the nature of the 

 instrument used, whether dredge or trawl — J. If, 



