ANOMIAD^. 
9 
i. 92) considers it as the ossification of the tendon of the adductor 
muscle. Mr. Broderip, in the passage quoted, regards it as a hone. 
In Dr. DieSeubach’s Travels Mr. Gray has remarked ; “ The plug 
is evidently only a modification of the kind of laminar beard formed 
by the end of the foot of the arcs {area) ; for, like it, it is formed of 
numerous, parallel, erect, longitudinal horny laminEe, placed side by 
side, extending from the apex to the margin, and it is on these 
plates that the calcareous matter is deposited when the attachment 
assumes its shelly substance. The same structure is to be observed 
in the plug of the European Anomia Ephippiuni {striata ).’' — Voy. 
New Zealand, ii. 261. 
Messrs. Forbes and Hanley compare it to the byssus of Pecten, 
and predict that when the very young Anomiae have been observed, 
they will be found to be attached by threads, like that genus {Brit. 
Moll.). The plug of a very small specimen of the genus is laminar, 
like that of the adult shell. 
M. Philippi, when describing Pododesmus, appears to have ob- 
served only the upper of the two muscular scars, for he gives as the 
generic character, “ Irnpressio muscularis unica, ovata,” and he only 
figures the larger upper one on the plate. 
The upper scar, which is usually of a larger size, and has its sur- 
face covered with radiating veins, while the lower is generally 
punctated, appears to be the one which gives rise to the muscle 
that is attached to the inner surface of the plug. 
The examination of the upper valve of a large series of specimens 
of Placunanomia patelliformis has shown that the position of the 
two muscles is liable to a slight variation ; in by far the larger num- 
ber of specimens the small lower muscle is quite close to and con- 
fluent with the scar of the upper larger muscle, but in a few speci- 
mens it is separated from the upper larger one by a small interval 
or space. Hence probably the three West Indian species of the 
genus may prove, when a larger series of specimens have been col- 
lected and compared, only varieties of the same species. 
* Shell plicately folded. Perforation of loiver valve small, firmly 
embracing the plug. Placunanomia. 
1. Pi .ACUNANOJIIA CuMlNGII. 
Shell depressed ; edge of the valves with three or four large an- 
gular folds. 
Placunanomia Cumingii, Broderip, Proc. Zool. Soc. 1832, 29; 
Sow. Genera, t. ; Manual, f. 189-191 ; Gray, P. Z. Soc. 1849, 
121 . 
Hab. Central America ; Gulf of Dulce, Province of Costa Kico. 
From Mr. Cuming’s collection. 
