Terebratula. 

 a Valve with the spiral arms, b Valve with arms 



removed. Terebratula digom. 



Terebratula Digona. Strophomeria Rugosa. 



Producta Martini. 



Strygoccpualus Burtini. 



Terebratula Dorsata. 



Terebratula \lata. 



Terebratula Deformis. 



Besides the orders now described as composing the class Conchifera, there is a very curious group which 

 should also be included in it, although established as a separate class by many naturalists. This is the 

 group of Brachiopoda, containing only three genera at present known, namely, Terebratula. Lingvla. and 

 Orbicula ; but formerly of much greater comparative importance. These animals have all bivalve shells, 

 differing in no essential particular from those of the Conchifera in general. The two former genera are 

 attached, however, by a footstalk proceeding from an opening in one of the valves near the hinge, to solid 

 substances. The Orbicula is attached, like an oyster, by one of its valves. But in the complexity of the 

 muscular apparatus provided for giving motion to the valves, they much surpass the highest of the other 

 Conchifera. There are not only several muscles provided for the closure of the shell, but another set to 

 open it — an organization which no other bivalves possess. The most peculiar part of their structure, and 

 that from which they derive their name, consists in the presence of two very long arms or tentacula, 

 between the origin of which the mouth is situated. These can be projected to a considerable distance 

 from the shell, or drawn in and coiled up spirally within it. They do not appear, however, to seize upon 

 prey; but rather, by means of the cilia with which they are fringed, to create currents which may bring 

 food to the mouth. In the Terebratula, these arms are affixed at their bases to a very curious framework 

 within the shell, the use of which is uncertain ; but it is believed to aid, by its elasticity, in separating the 

 valves from each other. This framework is most complex in the species in which the arms are shortest. 

 The species of Brachiopoda at present known, live at great depths in the ocean; and many of their pecui 

 liarities seem to have reference to that particular condition. They are distributed through all latitudes. ■ 



We furnish above a few specimens of this group of shells. 



