IS 



If the supposition that Aucella Piocldi is merely a synonym of A. 

 Mosquensis s]>ould prove to be well founded, the species has a very wide 

 geographical distribution, and a somewhat extended range in time. A. 

 Erringtoni may also be only another variety of this protean shell. 



Meleagrina amygdaloidea, (N. Sp.) 



Plate X., fig. 4. 



Shell inequivalved, left valve moderately convex, the right slightly 

 flatter; outline broadl}' elliptic-oval; height about one-third greater than 

 the length. Beaks rather small, curved forwards and downwards, placed 

 a little in advance of the centre of the valves. Escutcheon linear lanceo- 

 late, subcarinate at the margin, filled up, except at the extreme ends, by' 

 the thick ligament which projects above it in the centre. Hinge border 

 wingless, convex near the beaks, then sloping obliquely and rapidly 

 downwards. The posterior margin is broken, but it appears to have been 

 straight, and it forms a subangular junction with the hinge line above. 

 Anterior margin descending obliquely and widening outwards in a shal- 

 lowly concave curve which extends from the beaks to a point opposite to 

 the termination of the hinge line behind; very slightly convex in the 

 middle. The base, together with a small portion of the lower part of the 

 two sides, has almost exactly the shape of the widest end of a broad 

 ovoid. 



The sm-face of the test, which is very imperfectl}" preserved, appears 

 to be marked with faint, distant and rather irregular concentric strise, or 

 plications. 



Height, two inches and six lines ; length, one inch and nine lines ; 

 thickness, allowing for a part of the shell which is wanting on one valve, 

 one inch. 



A single specimen, with the posterior margin broken, but which 

 shows the large external ligament, and the test composed of an outer, 

 libro-prismatic layer, and an inner nacreous lining ; a combination of 

 characters almost peculiar to tlie Aviculinse. 



On the whole, this wingless Avieula is probably a rather aberrant 

 species of the Lamarckian genus Meleagrina, but it may prove to be the 

 tj\)e of a new sub-section. It is true that the shortness of the hinge 

 suggests affinities with Pseudoptera, as recently re-defined b}'- Meek,* but 



* " Report on the Invertebrate Cretaceous and Tertiary Fossilis of the Upper Missouri Country," 

 Washington : 1876. Pa^e 29. 



