AUCELLINA. 73 



Description. — Shell oval, very obli(|ue, very incciuivalve ; dorsal pai-t 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 eai- 

 usually of about the same length as the anterior ear, 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 umbo to the postero- 

 ventral extremity. Dorsal portion of the valve produced into a lai-ge, prominent, 

 much curved umbo. Hinge-area obtusely triangular. Posterior car 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 nnn. 



Height (oblique) 29 . 27 . 25 . 17 „ 



(1 — 4) Cambridf^e Greeusand. 



Affinities. — The probable relationship of this species to Aucella has l)een 

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

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

 Pompeckj, l)y whom the genus Aucellina has been established to include Avicida 

 aptiensis, d'Orbigny, and Avicula (jri/phieoidcs, Sowerby. Anrellina 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 Goquandianns, d'Orbigny, was regarded by Jukes-Bi-ownc as identical 

 with Aucellina riri/phasoides, and 1 agi'ee with that view. Tlie identity is also suji- 

 ported by the fact that Pictet and Campiche referred the specimens fouTid in (lie 

 Cambridge Greonsand to Inoceramus Coquandiainis. 



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

 collection of Mrs. Murchison, and came from the Upper Greeusand of Nurstt^-d 

 and Cambridgeshire (? Cambridge Greensand). 



Distribution. — Up])er Gault of Folkestone and Eastbourne. Red Limestone of 

 Hunstanton and Speeton. Cambridge Greensand (derived). 



L'^^pper Greensand (zone of 8chlaml>achia mstrata) of Hanqishire, Devizes, and 

 near Didcot ; (zone of Fecten asper) of Okeford Fitzpaine and ^Varminster. Cani- 



10 



