Hk/'ORT of rut: State GEOLOGIST. 



515 



variesfrom two or three (Lingula, Oyolospira) to twenty-five 

 (Spvrifer m/ucronafa 



In the majority of living forma (Liothyrina, Maqellania, 



M A..ASKU.A. Muhli eldtia, Kraussina, etc. etc.), ,,lr anns extend 

 forward from the month or oral disk to the anterior margin oi 

 the valves, recurving toward the mouth, and there formii 

 short unpaired spiral in the axial line. While these are the 

 principal variations in the arrangement of these parts, a notable 

 difference ispresented by 

 Megathyris, Theoidium/ 

 and their allies, in the com- 



plete attachment of the 

 arm to the brachial valve 

 by its lower margin. 

 The area thus inclosed 

 by the brachia is fre- 



-. , -w ,j . Fig. 142. -Brachial valve of Megathyris decollate*, showing 



queiltly large ymegatthyriS the arms attached by their lower margin about the 



decol!ata)l'dnd[it may be expanded oral disk, (woodward.) 

 divided on its outer margin into three or more deep lobes. 

 Living species whose brachia do not rest upon solid, 

 calcified supports may possess the ability to uncoil and protrude 

 the brachia between the open valves. This has been observed in 



Fig. 14$.-Craiiia anomala, with 

 arms extended . (Davidson.) 



Fig. 144. — Hemithyris psittacea, 

 with arm extended. 



Rhynchoxella (Owen, Morse), though it is doubtful if it is pos- 

 sible to the animal of Lingula. In Terebratulina caput-serpentis, 

 which possesses a short, solid brachial support, the animal can 

 extend only the outer free margins of the arms and then but for 

 a very short distance (Barrett). 



67 



