PAC. — YIN.] 



BRACHIOPODA. 



685 



Helopora alternata, H. mucronata, Ulrich, 

 1890, Jour. Cin. Soc. Nat. Hist., vol. 12, 

 p. 192, Trenton Gr. 



Nematopora conferta, N. granosa, N. ovalis, 

 Ulrich, 1890, Jour. Cin. Soc. Nat. Hist., 

 vol. 12, pp. 196, 197, Trenton Gr. 



Pachydictya emaciata, P. obesa, P. turgida, 

 Foerste, 1887, Bull. Denison Univ., vol. 

 2, pp. 162 to 165, Niagara Gr. 

 pumula, P. triserialis, Ulrich, 1890, Jour. 

 Cin. Soc. Nat. Hist., vol. 12, pp. 186, 187, 

 and in Micropalaeontology, pp. 42, 43, 

 P. hexagonalis and P. magnipora, Tren- 

 ton Gr. 



Paleschara quadrangularis,Nicholson, 1874, 

 (Chetetes quadrangularis,) Rep. Pal. 

 Prov. Ont., p. 61, Devonian. 



Pinacotrypa marginata, Whiteaves, 1892, 

 Cont. to Can. Pal., p. 278, Devonian. 



Polypora manitobensis, Whiteaves, 1892, 

 Cont to Can. Pal., p. 280, Devonian. 



Riiinidictya exigua, R. humilis and R. 

 minima, Ulrich, 1890, Jour. Cin. Soc. 

 Nat. Hist., vol. 12, pp. 183 to 185, Tren- 

 ton Gr. 



Rhombopora multipora, Foerste, 1887, Bull. 

 Denison Univ., vol. 2, p. 72, Coal Meas. 



Stictoporella rigida, Ulrich, 1890, Jour. 

 Cin. Soc. Nat. Hist., vol. 12, p. 188, 

 Trenton Gr. 



Stomatopora moniliformis, Whiteaves, 1891, 

 Cont. to Can. Pal., vol. 1, p. 212, De- 

 vonian ; S. tenuissima, Utica Gr. and 

 S. turgida, Hud. Riv. Gr., Ulrich, 1890, 

 Jour. Cin. Soc. Nat. Hist., vol. 12, 

 pp. 175 and 176. 



Subretepora halli and S. sublaxa, Ulrich, 

 1890, (Philloporina halli and P. sublaxa,) 

 Jour. Cin. Soc. Nat. Hist., vol. 12, pp. 

 179 and 181, Trenton Gr. Ulrich gives 

 his reasons for not using Subretepora 

 in vol. 8, p. 686, Geo. Sur. 111. 



Vinella, Ulrich, 1890, Jour. Cin. Soc. Nat. 

 Hist., vol. 12, p. 173. [Ety. proper 

 name.] Zoarium attached to foreign 

 bodies, consisting of exceedingly slen- 

 der, ramifying, thread- like tubes, occa- 

 sionally radiately arranged; surface 

 faintly lined longitudinally ; a row of 

 widely separated pores along the sur- 

 face of the tubes. Type V. repens, de- 

 scribed at the same time from the 

 Trenton Gr. 



•o+o» 



CLASS BRACHIOPODA. 



One valve of the shells in this Class is always larger than the other. A line 

 drawn vertically from the beak to the base will divide the shell into two equal parts. 

 The flattened space between the beaks is called the hinge area or the cardinal area ; 

 the aperture in one of the beaks is called the foramen ; and the triangular plate in 

 front of the foramen and sometimes forming part of its circumference is called the 

 deltidium, but in some genera it does not exist. Whan there are no teeth, as in 

 Crania, the valves are held together by the adductor muscles. The shells are found 

 in all Groups of rocks, from the Taconic to the most recent; but the Class seems to 

 have reached its maximum development in the Devonian, and to have slowly de- 

 clined since the Carboniferous age. 



Beecher says the main characters common to the Class are, the bivalve shell, 

 the pedicled or fixed condition, the animal composed of two pallial membranes inti- 

 mately related to the shell, a visceral sac, and two arms or appendages near the 

 mouth. The extreme range of variation does not eliminate any of these features, 

 and consequently no univalve or multivalve forms are found, nor any strictly free 

 swimming species, nor growths or modifications adapting the organism to a Pelagic 

 life. All Brachiopods have a common form of embryonic shell called the proteg- 

 ulum. (Ety. pro, early; tegos, a covering.) The protegulum is semicircular or 

 semielliptical in outline, with a straight or arcuate hinge-line, and no hinge area. A 

 slight posterior gaping is produced by the pedicel valve being usually more convex 

 than the brachial. The modifications noted are apparently due to accelerated growth, 

 by which characters primarily nealogic become so advanced in the development of 

 the individual as to be impressed finally upon the embryonic shell. 



