INVERTEBRATES. 343 



Myalina meliniformis, M. and W. 



PI. 27, fig. 3. 



Myalina meliniformis, Meek and Worthkn, March, 1866. Proceed. Chicago Academy 

 Sci., vol. i, p. 19. 



Shell rather small, mytiloid, very nearly equivalve, not 

 very oblique; posterior margin rounding down with a broad 

 regular curve from the extremity of the hinge; base rather 

 regularly rounded; anterior margin descending at rather less 

 than a right angle with the hinge, with a concave outline, 

 in both valves inflected so as to meet at a very obtuse angle ; 

 hinge rather short, arched, and ranging at an angle of about 

 60 ° with the longer axis of the valves ; beaks terminal and 

 directed forward, not projecting above the hinge; umbonal 

 slopes rounded, and curving down from the beaks near the 

 anterior side — scarcely as convex as the sides of the valves 

 just behind them. Cardinal area narrow and finely striated. 

 Muscular impressions distinct, subcircular, and placed a little 

 below and behind the middle of the valves; pallial scar well 

 defined, and extending from the lower anterior side of each 

 adductor impression a little forward, and then curving and 

 ascending near the anterior side of each valve, as a row of dots, 

 towards the beaks — posteriorly it ascends from the upper pos- 

 terior side of the adductor scar, in the same way. Surface 

 unknown. Length, from the beaks obliquely to the posterior 

 basal margin, 1.05 inch; breadth (antero-posterior diameter), 

 0.52 inch; convexity, 0.35 inch. 



We only know this species from internal casts, from which, however, it is 

 seen to differ materially from the last, in heing very much less oblique, and in 

 having no lobe-like projection, in front of the beaks. It is much more nearly 

 allied to M. permiana of Swallow, from which it differs in having its umbonal 

 slopes much less prominent, and more rounded, while the sides of its valves, 

 just behind and above these umbonal slopes, are more convex. In form.it is 

 almost an exact miniature of a large ponderous shell figured on page 33 of 



