1 88 MOLLUSCA. 



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

 is no enlargement of the alimentary canal, which can be re- 

 garded as a stomach, and the anus is a simple aperture situ- 

 ate on the side. There are marked indications of salivary 

 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 ventricles. 

 The gills themselves are arranged in a pectinated form, on 

 the inner surface of each lobe of the cloak. There is no- 

 thing 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 pe- 

 duncle, and pronounced them connected with the genus 

 Pinna. Bruguiere, aware of Seba's figure,"contemplated the 

 formation of the new genus for its reception, which Lamark 

 executed. M. Cuvier afterwards dissected one of the indi- 

 viduals, which Seba had possessed, and unfolded characters 

 in its organization, sufficient not only to warrant the con- 

 struction 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, 

 we do not consider the mere form of the shell as furnishing 

 characters sufficiently obvious and precise to warrant such 

 distribution. 



