AMERICAN JOURNAL 97 



Terebratella. — Apophyses with their hsemal arms con- 

 nected with the septum by two septal processes. 

 Trigo7iosemus. — Area large, flat ; beak produced ; fora- 

 men minute, apical. 

 Lyra. — Beak much produced, divided internally by the 



prolongations of the dental laminre. 

 Terebratella. — Shell usually ovate. Brachia with two 

 lateral lobes meeting behind the mouth, median 

 lobe absent, or obsolete. Septum not promi- 

 nent, posterior neural loop free. 

 Laqueus. — Shell ovate, foramen usually entire, posterior 

 neural loop attached on each side by slender 

 processes to the h?emal processes, near the at- 

 tachment of the septal processes. 

 Kingena. — Posterior part of the neural loop broad, angu- 

 lated, with the corners brought down and 

 attached to the septum. Exterior rough or 

 pustulate. 

 Ismenia. — Lateral loops and neural loop broad, and 

 blended posteriorly with the haemal and septal 

 processes, forming a broad funnel-shaped ring ; 

 lateral loops anteriorly open. Exterior as in 

 Terehratella. 

 Megerlea. — Apophyses as in Isfuenia, but lateral loops 

 closed with calcareous matter. Shell transverse, 

 hinge-line straight ; striate outside, pustulate 

 inside. Median brachial spiral lobe prominent. 

 Brachia passing behind the mouth. 

 Magas. — Apophyses attached by the sides of the haemal 

 processes to the septum. 

 Magas. — Reflected portion of the loop incomplete. 

 Magasella. — Reflected portion of the loop complete. 

 KRAUSSININ^. — No loop. Apophyses comprising two 

 laterally extended lamella attached to the 

 upper part of the prominent mesial septum 

 of the lifBmal valve. 

 Kraussina. — Shell externally sculptured, beak truncate ; 

 foramen large, incomplete ; septal lamellee an- 

 teriorly inclined. Mouth behind the brachia, 

 mesial spiral lobe minute. 

 BoucHARDiA. — Shell externally smooth, beak produced ; 

 foramen minute, complete ; septal lamellae pos- 

 teriorly inclined. 

 PLATIDIIN^. — Brachia sigmoid, meeting behind the mouth; 

 no spiral lobe. 



