NO. 5 RHYNCHONELLOID BRACHIOPODS — COOPER 63 



Brachial valve interior with prominent socket ridge to which the 

 short crural bases are attached without outer hinge plates. Crura 

 moderately long, of spinulifer type, nearly straight, compressed to 

 slightly crescentic in section and with distal extremities flattened ; no 

 inner hinge plates. Posterior of crural bases attached to floor of valve 

 by short plates ; cavity between plates occupied by callus, thus making 

 the apex solid. Median ridge or septum absent; adductor field 

 elongate. 



Type species. — Rhynchonella sicula Seguenza, in Davidson, Geol. 

 Mag., vol. 7, No. 76, p. 461, pi. 20, fig. 6, 1870. 



Comparisons. — This is a wedge-shaped form with fine radial orna- 

 mentation comparable to Hispanirhynchia, Grammetaria, and Comp- 

 sothyris. It differs from all these in the nature of the cardinalia. On 

 the inside of the brachial valve the cardinalia of Sephenarina differ 

 from all three in the almost total absence of a median ridge or septum 

 and in the fact that the plates supporting the crural bases at the apex 

 meet the floor of the valve directly. 



Geological horizon. — Pliocene of the Mediterranean region. 



Assigned species. — The following species are placed in this genus : 



Rhynchonella sicula Seguenza. 



R. soricina Defrance = R. sicula Seguenza. 



? Hemithyris eotrigona Sacco and variety obliquatella Sacco. 



Discussion. — This species has commonly been referred to Hispani- 

 rhynchia because of the close similarity of form and ornamentation. 

 In fact Jeffreys (1878, p. 413) identified dredged specimens of the 

 latter as identical with the Italian species. Examination of the beak 

 and brachial valve interior of R. sicula will dispel the idea of identity 

 almost immediately. 



The material of S. sicula showing interior details is scanty. The two 

 specimens in the National Museum from which the above description 

 was drawn were prepared by needles, a delicate operation considering 

 the thin shell of the species and the fragile nature of the cardinalia. 

 The length of the crura is moderate and the ends are flattened later- 

 ally, strongly suggesting the crura of Frieleia. 



The cardinalia of Sphenarina are suggestive of those of Hispani- 

 rhynchia but the median septum is lacking. The plates supporting the 

 crural bases thus rest directly on the valve floor rather than on the 

 median septum. A young specimen dissected shows no trace of a 

 septum and no evidence of supporting plates for the crural bases. 



