138 McLeam — Silurian Arisaig Series of Arisaig, JY.S. 



rounded, flabellate and excavated ventral muscle scar and 

 the short dorsal median septum are similar to Eatonia. 

 But certain Eatonia characters are not developed. 

 These are the radiating fine striae, the cardinal process 

 of crural origin and the ventral median septum. Proba- 

 bly ancestral to the Par eatonia forms of Eatonia at 

 least, but the later of the two Arisaig species referred 

 to this genus has developed concentric lamellae and hence 

 is off the main ancestral line. ' 



Genotype: Eatonioides lamellomatus, n. sp. 



Eatonioides lamellomatus, new species. 



The form of this species closely resembles that of 

 Eatonia {Par eatonia) medialis (Vanuxem). The dorsal 

 valve is more convex and the surface is ornamented, not 

 by radiating striae, but by concentric lamellae. The 

 generic characters have already been described. 



Width 25 mm., length 22 mm. 



Horizon and locality: Common in the Moydart forma- 

 tion, coast section, Arisaig, N. S. 



Plagiorhyncha, new genus. 



(Uxiyio lateral, referring to position of plate 

 bearing the teeth. ) 



Dorsal interior as in Camarotcechia Hall and Clarke, 

 but the teeth are not supported by a dental plate pro- 

 duced forward from the walls of the rostral cavity, but 

 are borne on a short plate arising from the lateral walls 

 of the ventral valve. Outline plicated biconvex, out of 

 which arise independently nearly smooth and also 

 striated species with shallow and marginally deflected 

 ventral valve. The following are referred to the new 

 genus : Rhynchonella glassii Davidson, Plagiorhyncha 

 plastica, n. sp., and Terebratula decemplicata Sowerby. 



Genotype: Rhynchonella glassii Davidson = Atrypa 

 depressa Sowerby. 



Class Pelecypoda Goldfuss. 



Superfamily Nuculacea. 



Honeymania, new genus. 



The flattened post-cardinal border resembles some of 

 the Limopsidae Dall and also some of the Lunulicardiidae 



