MOLLUSCA. 497 



has interspersed muscular fibres. Its margin is thickened, 

 and fringed with fine hairs of nearly equal length. 



The arms are fleshy in their substance, conical, elongat- 

 ed and compressed in their form, and ornamented on the ex- 

 ternal surface with thickset fringes or tentacula. The mouth 

 is simple, and situate between the arms at their base. 

 There is no enlargement of the alimentary canal, which can 

 be regarded as a stomach, and the anus is a simple aperture 

 situate on the side. There are marked indications of sa- 

 livary glands and a liver. The blood is conveyed to the 

 gills by two vessels, which are divided at the separation of 

 the lobes into two branches, one of these going to the half 

 of one lobe, and another to the opposite half of the other 

 lobe. Two systemic veins occupy a similar position, and 

 return the aerated blood to the two lateral systemic ven- 

 tricles. The gills themselves are arranged in a pectinated 

 form, on the inner surface of each lobe of the cloak. There 

 is nothing known of the nervous or reproductive systems of 

 this animal. 



The Lingula unguis is the only species of the genus, 

 and appears to be confined to the Indian seas. The valves 

 were first figured by Seba, together with the peduncle by 

 which they are supported. Linnaeus having seen only 

 one valve, conjectured that it belonged to Patella, and 

 named it P. unguis. Chemnitz examined both valves, 

 without the peduncle, and pronounced them connected with 

 the genus Pinna. Bugiere, aware of Seba's figure, con- 

 templated the formation of the new genus for its reception, 

 which Lamarck executed. M. Cuvier afterwards dissect- 

 ed one of the individuals, which Seba had possessed, and 

 unfolded characters in its organisation^, sufficient not only to 

 warrant the construction of a new genus, but a new class. 



Some petrifactions have recently been referred to this 

 genus ; but, in the absence of all vestige of the peduncle, 



VOL. II. I i 



