486 



Forty-fifth Beport on tee State Mvsevm. 



In the brachial valve the crura or bases of the brachial 

 processes may be supported by divergent vertical septa, known 



Fig. 74.— interior of pedicle-valve, of Orihi- 

 sinaanomala D, deltidium; t, teeth: d, dental 

 plates, forming a spondylium; s, median sep- 

 tum. (Davidson.) 



Fig. 75.— The interior of the pedicle-valve 

 of Conchidium; showing the spondylium. 



as the crural plates. These may also converge and form a 

 spondylium. Accompanying these, or independent of them, may 

 be a prominent median septum (Enteletes, 

 Kayserella, Pentamerus) ; and the latter 

 may support the spondylium. There may 

 also be two parallel median septa supporting 

 the convergent, but not united crural plates 

 (Barrandella, Pentamerus, Conchidium). In 

 the inarticulate genera the median and 

 lateral septa are sometimes well developed, 

 but do not often attain great size (Lingula, 



DlGNOMIA, (xLOTTIDIA, LlNGULASMA, etc.). 



Muscular scars. 

 The impressions made upon the shell by the 

 attachment of the muscles are usually confined to the umbonal 

 and posterior portions of the valves. There are some exceptions 

 to this rule, as in the case of Hipparionyx proximus and a few 

 members of theorthoid genus Rhipidomella, where thegreat scars 

 of the pedicle- valve extend almost to the anterior margin of the 

 shell. The impressions of the several muscular bands are 

 retained with various degrees of distinctness; among the fossils 

 they are often merged with one another, so that only the outline 

 of the muscular area, as a whole, is visible. Anions the articu- 

 late genera, one plan of arrangement is maintained without essen- 



36 



Fig. 76. — Lingula Delia 

 with median septum (s). 



