DISCONTINUOUS. 133 



longing to the family of Alatse, in the system of Lamarck, are 

 diffuse in the outer lip. Fig. 402 to 40G. 



DIGITATED. {Digitus, finger.) Branched out in long points, as 

 Ricinula, fig. 413. 



DILATED. Expanded, spread. This term has the same applica- 

 tion as diffuse and alated, explained above. The outer lip of 

 Rostellaria Columbaria, fig. 403 (Hippochrenes, Montf.), will 

 serve as an example. 



DIMORPHINA. D'Orb. A genus of microscopic Foraminifera. 



DIMYARIA. (Ate, dis, double ; fxvov, myon, muscle.) The first 

 order of Conchifera, Lam. including those molluscs which have 

 two adductor muscles, and consequently two muscular impressions 

 in each valve. The Conchifera Dimyaria are divided into Cras- 

 sipedes, Tenuipedes, Lamellipedes, and Ambiguse, fig. 44 to 

 155. 



DIOICA. Bl. The first division of the class Paracephalophora, 

 Bl. It is divided into the orders Siphonobranchiata and Asiphoni- 

 branchiata, Bl. 



DIPLODON. Spix. Hyria Syrmatophora, Lam. fig. 144, and 

 Unio multistriatus, Lea, are doubtfully quoted by Lea as belong- 

 ing to this apparently ill-defined genus of Nayades. 



DIPSAS. Leach. A genus or sub-genus of Nayades, the distinc- 

 tive character of which is " having a linear tooth under the dorsal 

 edge." D. plicatus, fig. 142. 



DISCINA, Lam. Orbicula, Auct. 



DISCODOMA. Sw. A sub-genus of Lucerninse, Sw. (Helix), thus 

 described, "teeth none ; aperture angulated ; the inner lip nearly 

 obsolete ; the outer only slightly thickened ; margin carinated." 



DISCOIDAL. {Discus, a circular plane.) A spiral shell is said to 

 be discoidal, when the whorls are so horizontally convolute as to 

 form a flattened spire. Ex. Planorbis, fig. 311. Orbulites 

 Discus, fig. 479. 



DISCOLITES. Montf. A genus of microscopic Foraminifera. 



DISCONTINUOUS. Interrupted. Ex. The siphon of Nautilus 

 is discontinuous, i. e. its termination in one chamber does not 

 reach to its commencement in the next. The varices of Triton, 



