ORDER IV 



TELOTREMATA 



341 



, Hall. Externally like Meristn, but. without spondylia. Ap-x 

 of jugum with two annular processes. Devonian ; North anl South America 

 ami Europe. 



Charionella, Billings. Similar to the last, but with a greatly modified 

 hinge-plate. Devonian ; North America. 



Pentagonia, Cozzens (Goniocoelia, Hall). Meristettae with a lr<> nl, angular, 

 sharply limited, ventral sinus and abrupt lateral slopes. Dorsal valve with 



FIG. 587. 



Mi-ritta herculea, Barr. sp. Devonian (F-); Konieprus, Bohemia. A, External aspect of ventral valve, 

 broken away near the apex so as to show the "shoe-lifter process," 1/1- #, Fractured shell showing median 

 septum ; spiralia destroyed (after Barrande). C, D, Frontal and lateral views of spiralia, slightly enlarged 

 (after Davidson). 



a wide, rounded fold, divided by a narrow sinus and umbo-laterally with two 

 short flanges. Devonian ; North America. 



Merista, Suess (Camarium, Hall), (Fig. 587). Like Meristella, but with a 

 spondylium. Silurian and Devonian ; Europe and North America. 



Dicamara, Hall and Clarke. Meristellae with a spondylium (" shoe-lifter 

 process ") and brachidium. Europe. 



Dioristella, Bittner. Similar to Meristella. Alpine Trias. 



Camarospira, Hall and Clarke. Like Meristella, but with a small spon- 

 dylium supported by a median septum, to which is attached only the pedicle 

 muscle. Devonian ; North America. 



Range and Distribution of the Brachiopoda. 



Owing to their great abundance, world-wide distribution, and remote 

 antiquity, as well as their excellent state of preservation, Brachiopods 

 occupy a very conspicuous rank among extinct Invertebrates, and furnish us 

 besides with a large number of important index fossils. The calcareous com- 

 position of their shells enables them to resist the destructive action of the 

 fossilisation process more successfully than the shells of Mollusks, which are 

 composed for the most part of aragonite. Their value as index fossils, 

 however, is somewhat detracted from owing to the difficulty of identi- 

 fying numerous genera, without a knowledge of their internal structure. 



The four orders into which the class is now divided are represented in 

 the lowest Cambrian, or Olenellus zone, indicating that Brachiopods had 

 their origin in Pre-Cambrian times. In the Lower and Middle Cambrian, 

 the Atremata and Neotremata predominate ; and although the Protremata are 

 known in the Lower Cambrian by very typical species, it is not until the 

 Upper Cambrian that the order becomes conspicuous. The Telotremata are 



