CHARACTERISTIC DEEP-SEA TYPES. - BRACHIOPODS. 75 



" Challenger " from the deepest water in which any bivalve has 

 yet been found living. 



There are almost innumerable illustra- 

 tions of beauty, adaptation, or unusual 

 characteristics which might be cited, but 

 to those unacquainted with the objects 

 themselves such an enumeration would 

 be tedious. The enthusiastic student and 

 collector alone can find pleasure in what 



! -, , , Fig. 312. Vesicomya 



would seem to most people a dry com- venusta. *f. 



bination of a lexicon and a catalogue. 



BRACHIOPODS. 



Until quite lately brachiopods were rarities in collections ; but 

 since the days of dredging expeditions we know that they are 

 very numerous at favorable localities on rocky or stony bottoms. 

 They do not seem to penetrate very great depths, naturally 

 finding no point of attachment in the soft ooze of the deep 

 waters, and but few species are thus far known to extend beyond 

 600 fathoms. The largest known species have been dredged 

 from the abyssal region, and young specimens are frequently 

 found attached to the older ones. None of the deep-water spe- 

 cies have the brilliant coloring characteristic of the common lit- 

 toral species belonging to the genus Lingula. The principal 

 differences upon which their classification is based are those of 

 the so-called loop, the calcified support of the brachia, and the 

 structural details of the valves. 



The recent brachiopods are specially interesting as represen- 

 tatives of a group which attained an extraordinary development 

 in very early ages, and has been represented in all formations. 

 They have a most extensive geographical distribution, and a 

 great bathymetrical range. They are found at all levels, from 

 pools left by the tides to a depth of 3,000 fathoms. The num- 

 ber of living species is small compared to the hosts which flour- 

 ished in the silurian, devonian, and carboniferous, from which 

 time they have steadily diminished in number. Nearly 1,700 

 species occur in the silurian, but there are not more than 120 

 known from the seas of the present day. Their position in the 



