SUMMARY 



GENERA OE CORNISH TESTACEOUS MOLLUSCS. 



SEDENTARY ANNULATA : With tubes or cases, encrusted with 

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

 homogenous. This order comprizes Dentalium, Sabellaria, Tere- 

 bella. Amphitiiie, Spirorbis, Serpula, Vermilia. Vermetus much 

 resembles the Serpulaceae, 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 sometime* with accessary plates 

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

 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 four Sections, 



C Crassipf.da : The shell when shut, gaping at the sides : Comprizing 

 the Genera Teredo, Fholas, Gastro<li3ena, Solen, Mya, Anatina. 



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

 prizing the Genera Lutraria, IMactra, Amphidesma, Corbula, 

 Saxicava, Venerirupis, Sanguinolaria, Psamonobia, Tellina, Lucina, 

 Donax, Capsa, Crassina. 



C. Lamzlupeda : 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, Cythersea, Venus, Cardium, 

 Hiatella, Iso-cardia, Area, Pectunculus, Nucula, Unio, 



C. Ameigua or 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, Mytilus. Pinna, Avicnla. 



Second, Ligament not marginal, contracted into a short space 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. 



