218 Zoological Society. 



hole by the upper part of the anterior lobe of the notch being sol- 

 dered to and forming part of the cardinal edge : the plug triangular, 

 gradually enlarging in size ; the apex and outer surface next to the 

 body to which it is attached, calcareous, longitudinally striated ; the 

 inner surface covered with horny, longitudinal, parallel laminae, and 

 more or less agglutinated to the edge of the notch. 



Syn. Placunanomia, Broderip, Proc. Zool. Soc. 1832, 29 ; Miiller, 

 Syn. 176 ; Desk, in Lamk. Hist. vii. 269. 



Anomia, /3, Schumacher, Essai, 1817. 



Anomia, pars, Blainv. Man. Moll. ; Montague ; Forbes ^ Hanley. 



Ostrea, sp. Da Costa ; Montague. 



Placunonomia, D'Orb. Am^r. M6rid. 



Placunomia, Swains. Malac. 39, 1840. 



Pododesmus, Philippi, Wiegmann Arch. i. 385, 1837. 



Mr. Broderip, who established this genus, does not observe the 

 character furnished by the muscular impressions, or the lobe of the 

 notch : he merely says, " Impressio muscularis in utraque valva sub- 

 centralis. In valva superiore organi adhesionis impressio superad- 

 dita." And further, that " the organ of adhesion, which in its bony 

 character (for it is more bone than shell) resembles that of Anomia, 

 does not perforate the lower valve directly, but is inserted between 

 the laminae of the internal surface of the lower valve, above the mus- 

 cular impression and below the hinge, and passes out into an ex- 

 ternal, irregular, somewhat longitudinal, superficial fissure or cica- 

 trix, which is narrowest at the hinge margin, and which it entirely 

 fills to a level with the surrounding surface." 



This form is produced by the gradual increase of the size of the 

 plug and the simultaneous increase of the size of the shell. 



Some have considered the "plug" or "stopper" oi Anomia to be a 

 third valve, which is evidently a mistake. Philippi {Moll. Sicil. i, 92) 

 considers it as the ossification of the tendon of the adductor muscle. 

 Mr. Broderip, in the passage quoted, regards it as a bone. In Dr. 

 Dieffenbach's Travels I have remarked : " The plug is evidently only 

 a modification of the kind of laminar beard formed by the end of the 

 foot of the Arcs {Areas) ; for, like it, it is formed of numerous parallel, 

 erect, longitudinal horny laminse, 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 Ephippium {striata)." — Voy. Neio Zealand, ii. 261. 



Messrs. Forbes and Hanley compare it to the byssus of Pecten, 

 and venture to predict that when the very young Anomise have been 

 observed, they will be found to be attached by threads like that genus 

 {Brit. Moll.). I have examined a very small specimen of the genus, 

 and found it 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, "Impressio 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 surface 



