650 



BRACHIOPODA. 



leads to a slightly-coiled intestine, which may have an anus (TJLIETESTERATA), 

 or may not (CLISTEKTEIIATA). 



D 



7. 5; A NON-HINGED BRACHIOPOD (Lingula anatina). In- 

 terior of ventral (F.) and dorsal (D.) valves, showing muscle 

 gears, named as follows : u., umbonal; p.s., parietal; <.?,., 

 transmedian ; e.-L, externo-lateral ; m.-l., medio-lateral ; c., 

 centra? ; a.-Z., antero-lateral. Natural size. 



The Brachiopoda possess a system of blood-vessels, with a contractile heart, 

 a distinct nervous system, and a pair of excretory organs (nephridia), which 



serve also for the transmission of the 

 generative products. The sexes are 

 usually separate, But Lingula is 

 hermap hrodite. 



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. A few 

 (e.{/., Livujula, Fig. 2) bury them- 

 selves in mud ; but most attach 

 themselves to rocks. They occur in 

 great numbers wherever found. 

 Their shells, which are easily pre- 

 served, abound in strata of all ages, 

 so that a knowledge of them is of 

 great assistance to the geologist. 



The simplest form of Brachiopod 

 known occurs in the Lower Cambrian 

 rocks of America, and is called 

 Pater ina (Fig. 7). Its valves are 

 oval in outline, with 'one side truncated by a straight hinge-lino. Concentric 



Fig. 6. Internal organs of a Brachiopod 

 (Rhynchonclla psittacea). p., peduncle; 

 D. V. , dorsal valve, and V. V. , ventral valve, 

 of the shell, which are broken away on one 

 side, exposing L.,lophophore; M,, median 

 partition ; Oe., oesophagus, leading from a 

 mouth between the coils of the lophophpre 

 to the stomach, S.; C., the coecum, or blind 

 end of the gut, which has no anus. 



