122 MONOMYARIA. 



ORDEE I -MONOMYARIA. 



The animal provided with one muscle of attachment, 

 leaving a nearly central impression in each valve of the 

 shell. 



Section I. — Ligament either unknown, or forming a 

 tendinous tube, which connects the valves. 



TRIBE I. BRACHIOPODA. 



Animal with two opposite, elongated, ciliated arms, situ- 

 ated near the mouth, and rolled up spirally when the animal 

 is at rest; mantle having two separate lobes in front, which 

 envelop the body. Shell bivalve, adhering to extraneous 

 marine bodies, either by the shell itself being in contact 

 with them, or attached by a tendinous chord. The shells 

 are not quite equivalve, and open by a hinge. 



Genus 1 — LINGULA — Lamarck. 



Generic Character Subequivalve, flat, ovato-oblong, 



truncated at the apex, slightly pointed at the base, elevated 

 on a fleshy tendinous peduncle, attached to marine bodies ; 

 hinge without teeth. 



Lingula anatina The Duck Ltngula. Plate XIV. fig. 



7. Shaped like a duck's bill, with a green, shining epidermis, 

 and having a cylindrical pedicle from two to four inches long. 

 Inhabits the Indian ocean. 



Genus 2.— TEREBRATULA.— ZamorcA. 



Generic Character. — Inequi valve, regular, subtrigonal; 

 attached by a short pedicle to extraneous marine bodies; 

 the larger valve with a projecting umbo, frequently curved, 

 and perforated at its summit by a round hole, or a notch ; 

 binge with two teeth; two slender osseous processes arising 

 from the disk of the smaller valve internally. 



