BRACHIOPODA. 183 



444. Median sinus and fold present ; brachidium when present, a 



spiralium oo. 



00. Beak of pedicle valve truncated by a foramen. Shell 



transversely elongate ; spires extraverted I2f. 



I2f Plications covered with minute spines. 



CXI II. Parazyga. 



I2f Plications without spines CXII. Trematospira. 



00. Beak of pedicle valve not truncated by a foramen I3f. 



I3f Shell with faint radiating striae ; spirals extraverted. 



CXXIV. Meristella. 

 I3f Shell radially plicate; spirals absent, or when present 



not extraverted 12*. 



12* Plications confined to anterior portion of shell ; 



spiralium absent LXII. Camarella. 



12* Plications covering whole shell , I3 // . 



I3 // Sinus on pedicle valve and fold on brachial ; 

 spirals pointing into pedicle valve. 



CXVIII. Anoplotheca. 

 I3 // Sinus on brachial valve and fold on pedicle; 

 spirals pointing inward (introverted). 



XCVII. Zygospira. 



444. Median sinus and fold not present pp. 



pp. Beak of pedicle valve truncated by a foramen ; deltidial 



plates visible I4f. 



14-f- Shell with faint radiating striae; brachidium a loop, 



deltidial plates minute XCIII. Terebratulina. 



I4f Shell with coarse plications ; brachidium a loop, delti- 

 dial plates moderate XCVI. Terebratella. 



I4f Shell radially plicate ; brachidium of extraverted 

 spires, deltidial plates pronounced, commonly co- 

 alesced 13*. 



13* Plications rather coarse CXI. Hustedia. 



13* Plications fine or striate I4 // . 



I4 // Deltidial plates uncoalesced. 



CX. Homceospira. 



I4 // Deltidial plates coalesced d". 



d". Surface plicate CIX. Rhynchospira. 



d". Surface striate CXIV. Eumetria. 



pp. Beak of pedicle valve not truncated by a round foramen. I5f. 

 I5f Brachidium a spire turned into the extremely convex 

 brachial valve ; plications rounded, low. 



XCIX. Atrypa. 



I5f Brachidium a loop 14*. 



14* Length greater than breadth ; plications fine. 



LXXXVIII. Renssellaeria. 



14* Subcircular; plications angular, prominent ; small 



well defined cardinal area and deltidial plates 



on pedicle valve XCVI. Terebratella. 



II. Cardinal area present, straight. Hinge line straight and long, usually more 

 than one third the greatest width of shell 4. 



