BRACHIOPODA. 467 



lar, encroaching on both valves ; interior of dorsal valve as in Thecidimn, 

 with a single central septum and broad margin. Fossil. Lias — G. Oolite, 

 3 sp. Brit. 



Anoplotheca, (lamellosa) Tr. Sandberger, 1856. Dev. Rhine. = 

 Atrypa. 



jMeganteris, Suess, 1856. Terebratula Archiaci, Vern. Devonia7i, 

 Asturias. Shell with a long, reflected, internal loop. 



CONCHIFERA. 



Development. — The observations of Dr. Loven on the development of 

 Cavdiuni pygmcEum and Crenella marmorata (referrred to at p. 51, note) 

 have been confirmed by M. M. Keber and Webb, who observed similar phe- 

 nomena in the ova of the river-mussel {Anodon). The body described by 

 Loven as the nucleus of the germinal vesicle is regarded by these later 

 observers as a tubular orifice, analogous to the micropyle in the vegetable 

 ovum, by which the spermatozoa penetrate the yolk. 



In Anodon the embryouic mass divides, partially, into two halves, each 

 having its own mouth and intestine ; and its own distinct though simple heart ; 

 and it is by the approximation and ultimate fusion of the two ventricles that 

 the common rectum of the originally distinct intestines is intercepted. 

 (Quatrefages, — Loven.) 



OsTREiD^, p. 253. The union of the Ostreidce and Pecthdda, as proposed 

 by the authors of the " History of British Mollusca," has not proved satis- 

 factory. The genus Ostrea stands quite alone, and distinct from all the 

 Pectinidce in the structure of its gills, which are like those of Avicula, and by 

 resting on its left valve. The shell also is more nacreous than that of the 

 scallops. 



Dimya (Deshayesana) Rouault, 1859. Mem. Soc. Ge'ol. b. III. 471. 1. 15. 

 fig. 3. L. Eocene, Paris. The figure is most like an oyster, and the 

 " second adductor impression," on account of which it is named Dimya, is 

 rather like the small anterior scar in Pecten (fig. 173, p. 249). 



Placuna^ is essentially like Anomia, having the generative system attached 

 to the right mantle-lobe, and the ventricle exposed. The mantle-margin is 

 cirrated, and furnished with a curtain, as in Pecten ; the foot is tubular and 

 extensile, but has no distinct muscles except the small one, whose existence 

 in P. placenta (PI. XVI. fig. 6) we had predicated from examination of the 

 shell (p. 256).t The small muscular impressions before and in the rear of the 

 adductor are produced by suspensors of the gills. 



Anomia. The description given at p. 255 requires correction; the lips 



* Original figures and descriptions will be found in the An. Nat. Hist. 1855, p. 22. 

 + This organ appears to represent the hyssal-shealh of Anomia, rather than the 

 ■foot, as there is no other opening for the passage of a byssus. 



