j 8 The Irish Natuialist. [April, 



It is a fact to be carefully noted that the most ancient types 

 of these fossils bear the impress of an organization as high as 

 that of their descendants now living. It has been remarked 

 in particular that the specialisation of the muscles, as indi- 

 cated by their scars in the shells of the earliest genera — 

 Lingula <?.£.— points to a remote ancestry in pre-Cambrian 

 times of which no traces have been, or, it may be added, are 

 ever likely to be found. 



The Brachiopoda reached the acme of their numerical 

 development in the Ordovician and Silurian seas, and after 

 that they gradually declined, though in the Carboniferous 

 period they were still fairly numerous. At present there are 

 very few species, and these are distributed in all seas, tropical, 

 temperate, and arctic. I have myself dredged the Parrot's- 

 bill Rhynchonella (R. psittacca), an arctic species, in the Gulf 

 of St. Lawrence. 



There are two divisions of the Brachiopoda — those having 

 hinged valves, or Testicardinate Brachiopoda. as Rhynchonella, 

 and those having hingeless valves, or Ecardinate, as Lingula. 

 A few words as to the animal. The body, which is bilaterally 

 symmetrical, is comparatively small ; two folds or flaps, con- 

 stituting the mantle, spring from it ; chitinous bristles (setae) 

 are often implanted in its thickened edge, and from the pos- 

 terior end (the narrow end in the shell) the stalk or peduncle 

 arises by which the animal attaches itself to rocks or other 

 hard substances on the sea-bottom ; and in the case of Lingula, 

 this organ is used to draw the animal by its sudden contrac- 

 tion rapidly into its burrow when disturbed. The animal has 

 well- developed muscular, nervous, and vascular systems, but 

 sight is wanting, except in the larva, which has "eye spots." 

 But that these animals are sensitive to light is shown by what 

 Lacaze-Duthiers has related of them. He w 7 as watching a 

 vessel containing Thccidium (Testicardinates) when, as his 

 shadow fell upon them, they all closed their valves, which had 

 before been gaping open. The shell, calcareous in the hinged 

 Brachiopods, chitinous in some of the hingeless ones, consists 

 in the former of two pieces or valves which are symmetrical 

 in themselves, but one (the ventral) is usually larger than the 

 other (the dorsal), behind which it projects with its pointed or 

 beak-like apex, The beak is perforated, or there is in any 



