S U M M ARY 



or THE 



GENERA OF CORNISH TESTACEOUS MOLLUSCS. 



SEDENTARY ANNULATA : With tubes or cases, encrusted with 

 grains of sand and fragments of shells ; or solid, calcareous and 

 homogenous. This order comprizes Dentalium, Sabellaria, Tere- 

 bella, Amphitrite, Spirorhis, Serpula, Vermilia. Vermetus much 

 resembles the Serpulaceze, but is separated on account of the different 

 structure of the animal. 



C1RRHIPEDA, or BARNACLES ; With many valves or plates, sessile 

 or on a footstalk. From an opening capable of being closed proceed 

 many slender, jointed, fringed tendrils, which are organs of prehen- 

 sion. It comprizes Tubicinella, Balanus, Acasta, Creusia, Pyrgoma, 

 which are sessile ; and, with footstalks, the Genera Anatifera and 

 Pollicipes. 



CONCHIFERA or BIVALVES : With two principal valves or plates 

 united by a hinge or ligament ; and sometimes with accessary plates 

 not belonging to the valves. It is divided into two orders ; Cdn- 

 chifera Bimusculosa, with two internal separate and lateral muscular 

 impressions ; and Conchifera Unimusculosa, with only one muscle, 

 which appears to pass through the body : the impression being about 

 the centre of the shell. 



The first order, C. Bimusculosa, comprizes/our Sections, 



C Crassipeda : The shell when shut, gaping at the sides : Comprizing 

 the Genera Teredo, Pholas, Gastrochaeua, Solen, My a, Anatina. 



C. Tenuipeda: Gaping of the shell at the sides generally little: Com- 

 prizing the Genera Lutraria, Mactra, Amphidesrna, Corbula, 

 Saxicava, Venerirupis, Sanguinolaria, Psamonobia, Telliua, Lucina, 

 Donax, Capsa, Crassina. 



C. Lameli.ipeba •. Gaping none, but it is chiefly distinguished by the 

 structure of the animal ; the foot being broad and thin : Comprizing 

 the Genera Cyclas, Pisidium, Cyprina. Cytheraea, Venus, Cardials, 

 Hiatella, Iso-eardia, Area, Peetunculus, Nucula, Unio, 



C Ambigua on chamacea : The valves unequal, irregular : the hinge 

 with one thick tooth, or toothless The genus Isocardia was 

 comprized in this section, but is now removed ; there remains in it 

 therefore, no British species. 



The second order, C. Unimusculosa comprizes three Sections, 



The first, with the Ligament marginal, sublinear, elongated on the 

 edge : comprizing the Genera Modiola, Mvtilus, Pinna. Avicula. 



Second, Ligament not marginal, contractt-d into a short spare below 

 the beaks, visible, and not forming a tendinous cord under the shell ; 

 valves unequal, either in size or shape. It comprizes the Genera Lima, 

 Pecten, Ostrea, Anomia. 



Third, Ligament none, or formed by a tendinous cord supporting the 

 shell : comprizing the Genus Terebratula. 



