﻿202 T. Davidson — What is a Brachiopod ? 



bution of the recent species, as well as to the marine depths they 

 inhabit or prefer/ 



This important knowledge is mainly due to the numerous well- 

 conducted and equipped dredging expeditions carried on by private 

 individuals, and by the Governments of the leading maritime States.. 



Previous to these investigations the data we possessed with respect 

 to the habitat, and ranges of depth were, in most cases, vague and 

 unsatisfactory. It has also, been ascertained that the Brachiopoda are 

 much localised, and usually occur in great numbers in their favourite 

 haunts. 



We can know nothing with certainty in respect to the ranges of 

 deptli at which the extinct species lived ; but some idea as to their 

 probable depths can be surmised from a study of recent forms. 



As far as our present information will carry us, the Tretenterata 

 (Lingiila, etc.) do not appear to have been found at a greater depth 

 than from 1366 to 2000 fathoms. 



Lingula abounds in particular haunts, and lives at about half tide- 

 mark, and partly buried in mud ; or at depths varying from three or 

 four inches from the surface of the sea to seventeen fathoms. Prof. 

 Morse describes a species which he found in vast numbers in a sand- 

 shoal at lo w- water : the peduncle, six times the length of the shell, 

 was partly encased in a sand tube (PI. X. Fig. 5). He observed 

 likewise that this species (Lingula pyramidata) had the power of 

 moving over the sand by the sliding motion of the two valves, using 

 at the same time the fringes of setee, which swing promptly back and 

 forth like a galley of oars, leaving a peculiar tract in the sand. In 

 the motion of the setee he noticed the impulse commencing from 

 behind, and running forward. 



Discina has been found attached to stones at low- water mark, and 

 has been dredged from depths ranging from five to nearly 2000 

 fathoms; very often clustered together in vast numbers, and adher- 

 ing, in all stages of growth, by their peduncle to the surface of 

 the shell of their neighbour, one above the other, till they formed a 

 living mass of considerable breadth and thickness. 



Crania is found in great numbers adhering to stones and shells at 

 depths of from eighteen to 530 fathoms. Lucas Barrett informs us 

 that the cirri are protruded, but not the brachial appendages, beyond 

 the margin of the shell, and that the valve opens by moving upon 

 the straight side of the hinge without sliding the valve. 



The genera and species of Clistenterata lived at depths ranging 

 from about half tide-mark to 2600 fathoms. At that great deiDth, 

 between K.erguelen Island and Melbourne, the "Challenger" Ex- 

 pedition brought up, among other things, " a very elegant little 

 Brachiopod ;" another species was dredged by the same expedition 

 three hundred miles east of St. Paul's Eocks, Atlantic, at a depth of 

 1850 fathoms, but the larger number of species live at depths of 

 from five to three, or four hundred fathoms, usually attached by their 



' The reader is referred to an important paper upon this subject by Prof. Edward 

 Suess, iiber die Wohnsitze der 15rachiopoden (Aus dem xxxvii. und xxxix. Bande, 

 Wien, 1859, 1860, Akademie der Wissenschaflenbesonders abgedruckt). 



