188 MOLLUSCA. 
yet ge en 
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 isa 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 aérated 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. Linnzus 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. Bruguiére, 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. 
