306 BRACHIOPODA. 



accumulated granules deposited one after the other would result 

 in the peculiar shell formation of the Brachiopoda." The 

 extremities of the prisms are not visible on the external surface, 

 but in the young individual of some species, as Terehratula 

 caputserpentis, there is a thin layer of calcareous matter, which 

 seems to show that in some brachiopods the shell is composed 

 of two layers of shell, having a different structure, as in the case 

 of the Conchifera. 



The Lamp-shells are all natives of the sea. They are found 

 hanging from the branches of corals, the under sides of shelving 

 rocks, and the cavities of other shells. Specimens obtained 

 from rocky situations are frequently distorted, and those from 

 stony and gravelly beds, where there is motion in the waters, 

 have the beak worn, the foramen large, and the ornamental 

 sculpturing of the valves less sharply finished. On clay beds, 

 as in the deep claj^ strata, they are seldom found ; but where the 

 bottom consists of calcareous mud they appear to be very 

 abundant, mooring themselves to every hard substance on the 

 sea-bed, and clustering one upon the other. 



Of all mollusca the Brachiopoda enjoy the greatest range both 

 of climate, and depth, and time ; they are found in tropical and 

 polar seas; in pools left by the ebbing tide, and at the greatest 

 depths hitherto explored by the dredge. At present compara- 

 tively few recent species are known ; but many more will probably 

 be found by dredging in the deep sea, which these shells mostly 

 inhabit. The number of living species is already greater than has 

 been discovered in any secondary stratum, but the vast abund- 

 ance of fossil speciviens has made them seem more important 

 than the living types, which are still rare in the cabinets of 

 collectors, though far from being so in the sea. Above 4000 

 extinct species of Brachiopoda have been described, of which 

 a large proportion are found in Europe. They are distributed 

 throughout all the sedimentary rocks of marine origin from the 

 Cambrian strata upwards, and appear to have attained their 

 maximum of specific development in the Silurian age. Some 

 species (like Atrypa reticularis) extend through a whole 

 " system " of rocks, and abound equally in both hemispheres ; 

 others (like Spirifera striata) range from the Cordillera to the 

 Ural mountains. One recent Terebratula (caputserpentis ) made 

 its appearance in the Miocene Tertiary ; whilst others, scarcely 

 distinguishable from it, are found in the Upper Oolite and 

 throughout the Chalk series and London Clay. — Woodward. 



