ATTCELLINA. 7:'. 



Description.— Shell oval, very oblique, very inequivalve ; dorsal pari of posterior 

 margin more or less straightened, the remaining- margins forming a regular curve. 



Right valve flattened, but convex near the umbo; height and length nearly 

 equal. Umbo small, near the middle of the hinge-line, curving slightly. Hinge- 

 area obtusely triangular. Anterior ear long, triangular, with a very deep, narrow, 

 curved byssal sinus on each edge of which is a row of tubercles. Posterior ear 

 usually of about the same length as the anterior car, but indistinctly limited, with 

 the outer angle obtuse. 



Left valve convex, especially the dorsal part, more compressed postero-ven- 

 trally, sometimes with a shallow sulcus extending from the unibo to the postero- 

 ventral extremity. Dorsal portion of the valve produced into a large, prominent, 

 much curved umbo. Hinge-area obtusely triangular. Posterior ear larger than 

 the anterior, with a rounded depression between it and the umbo ; anterior ear 

 short, triangular. 



Ornamentation consists of numerous concentric growth-lines which sometimes 

 become lamellar, and are separated by flat interspaces. Small, close-set, radial 

 ribs occur, especially in the neighbourhood of the umbo. 



Measurements of left valve : 



(1) (2) (3) (4)' 



Length . . 22 . 21 . 18 . 14 mm. 



Height (oblique) 29 . 27 . 25 . 17 „ 



(1 — 4) Cambridge Greensand. 



Affinities. — The probable relationship of this species to Aucella lias been 

 pointed out by von Strombeck, Stoliczka, and Jukes-Browne. Recently its 

 affinities to Pseudomonotis and Aucella have been fully discussed by Prof. 

 Pompeckj, by whom the genus AucelUna has been established to include Avicula 

 aptiensis, d'Orbigny, and AvicuLi gryphaeoides, Sowerby. AucelUna is very closely 

 allied to Aucella, but differs from it in the absence of an articulating groove in 

 the hinge-area of the left valve. 



Inoceramus Ooquandianus, d'( )rbigny, was regarded by Jukes-Browne as identical 

 with AucelUna gryphaeoides, and I agree with that view. The identity is also sup- 

 ported by the fact that Pictet and Campiche referred the specimens found in the 

 Cambridge Greensand to Inoceramus Goquandiavus. 



Types. — I have not seen the types; Fitton stated tliat they were in the 

 collection of Mrs. Murchison, and came from the Upper Greensand of Nursted 

 and Cambridgeshire (? Cambridge Greensand). 



Distribution. — Upper Gault of Folkestone and Eastbourne. Red Limestone of 

 Hunstanton and Speeton. Cambridge Greensand (derived). 



Upper Greensand (zone of SchloenbacMa rostrata) of Hampshire, Devizes, and 

 near Uidcot ; (zone of Pecten a,sper) of Okeford Fitzpaine and Warminster. Cam- 



lo 



