144 BIPJ-USE. 



tlie-JimLo ; the other valve auriculated, with an obtuse umbo ; 

 hinge without teeth. — Obs. The green sand fossils contained in 

 this genus differ from Plagiostoma in being attached. D. striata. 

 PL X. f. 175. 



DIAPHANOUS. (Aia, dia, through ; <paiv(o, pkaino, to shine.) 

 Transparent. 



DIAPHEiAGrM. {^lafpayi^m, a partition.) This term is apj^lied 

 to the septa, by which the chambers of mnltilocular and other 

 shells are divided from each other. 



DICEEAS. Lamarck. (Ave, clis, double ; Kspac, ceras, horn.) 

 Fam. Chamacea, Bl. and Lam. — Bescr. Ineqiiilateral, inequi- 

 valve, attached by the point of the umbo of the larger valve ; 

 umbones prominent, spirally twisted and grooved ; hinge with 

 one large thick tooth in the larger valve ; muscular impressions, 

 two in each valve. — Ohs. The prominent spiral umbones, which 

 gives to this genus its name, with the circumstance of its 

 being attached by the point of one of them, is sufficient to 

 distinguish it from any other. Although it appears to approach 

 Isocardia in some characters, in others it will be found still 

 more nearly to resemble Chama. In fact, from being attached 

 and irregular, the shells composing this genus have been re- 

 garded as Chamse with produced umbones. The singular fossil 

 shells composing this genus, are found in granular limestone, 

 near Geneva in Normandy. D. perversum. PI. is. fig. 154. 



DICH^LASPIS. Darwin. Cirrip, p. 115. Octolasmis, 

 Gray. Heptalasmis, Leach. A genus of pedunculated 

 cirripides, the shell of which is thus described : " Valves 5, 

 generally appearing like 7, from each section being divided into 

 two distinct segments, united at the rostral angle ; carina gene- 

 rally extending up between the terga, terminating downwards in 

 an imbedded disc, or fork, or cup." Ex. D. Warwickii (imper- 

 fect figure.) PI. 2. f. 41. 



DIDONTA. Schum. Saxicava. Auct, 



DIPPUSE. {Biff'undo, to spread out, to dilate.) A term applied 

 to the aperture of a imivalve shell, when it is spread out or 

 widened into a flat surface, or digitations. Alated is anotlier 



