BRACHIOPODA. 



Ill 



called the " lopliopliore " (tuft-bearer), and resembles the 

 structure of the same name in the Bryozoa (Diagram 8). 

 The lopliopliore is generally produced into two so-called 

 arms/' which fill the forepart and sides of the shell-cavity 

 and are often spirally coiled. Since they were formerly 

 supposed to represent the " foot " of the Mollusca, tlieir 

 presence suggested the name Brachiopoda (arm-feet). The 

 mouth leads to a slightly coiled intestine (Diagram 10), which 

 in the simpler genera is provided with an anus, whence the 

 Class comprising them received the name Tretenterata 

 (pierced guts). Fossils indicate that some of the earlier 

 genera of the other Class were also provided with an anus ; 

 but in its later genera this structure became degenerate, and 

 no longer exists in the living representatives ;. for this 

 Class, therefore, the name Clistenterata (closed guts) was 

 proposed. These names are now generally supplanted by 

 Inarticulata and Articulata (see p. 112). 



The Brachiopoda are found in seas all over the world, 

 and usually at depths of less than 100 fathoms, but they 

 have been dredged at a depth of 2,900 fathoms. Most kinds 

 attach themselves permanently to a hard bottom by the 

 peduncle, open their shell so far as the hinge permits, and 

 collect minute food-particles in the currents of water that 

 flow down the lophophore ; some protrude and even unroll 

 the arms. Lingula, as shown in Diagram 2, lives in a tube 

 in the sand, forming a case of agglutinated sand round the 

 lower end of its peduncle ; it stretches its shell to the opening 

 of the tube, and the projecting setse guide the currents of 

 water down to the lophophore ; but when disturbed, the 

 peduncle contracts and the shell is withdrawn into the tube, 

 which closes in above. It is not, however, to be inferred 

 that all extinct species of Lingula and of similar genera 

 lived in this way. 



Though brachiopods usually occur in great numbers 

 wherever found, they are not so numerous now as they were 

 in past ages. In the Carboniferous Epoch especially, the 

 number of species and individuals was very great, and the 

 Producti then living reaohed a larger size than any brachiopod 

 before or since. Terebratula grandis, of the Coralline Crag, 

 is the largest brachiopod found in later rocks. Many 

 examples of masses of brachiopod shells are exhibited, and 

 among them may be mentioned a slab covered with Lingu- 

 lella Davisi, from the Lower Lingula Llags of Upper Cam- 

 brian Age, near Tremadoc ; Ungulite Grit with Oholus and 



Gallery 

 VIII. 

 Wall-case 

 11. 



Wall-case 

 10c. 



Wall-ease 

 10. 



Table-case 

 17. 



Wall-ease 

 10a 

 & 

 10b. 



