ORDER IV TELOTREMATA 341 
Meristella, Hall. Externally like Merista, but without spondylia. Apex 
of jugum with two annular processes. Devonian ; North and South America 
and Europe. 
Charionella, Billings. Similar to the last, but with a greatly modified 
hinge-plate. Devonian; North America. 
Pentagonia, Cozzens (Goniocoelia, Hall). Meristellae with a broad, angular, 
sharply limited, ventral sinus and abrupt lateral slopes. Dorsal valve with 

Merista herculea, Barr. sp. Devonian (F2); Konieprus, Bohemia. 4A, External aspect of ventral valve, 
broken away near the apex so as to show the ‘‘shoe-lifter process,’1/;._ B, 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. Jeristellae with a spondylium (“ shoe-lifter 
process”) and brachidium. Europe. 
Dioristella, Bittner. Similar to Weristella. Alpine Trias. 
Camarospira, Hall and Clarke. Like JMeristella, but with a small spon- 
dylium supported by a median septum, to which is attached only the pedicle 
muscle. Devonian ; North America. 
ae 
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 diviced 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 
