26*2 MOLLUSCA. 



MALLEUS, Lamarck. 



A simple pit for the ligament, as in the Ostrese, where the Mallei were left by 

 Linnaeus, on account of their having the same irregular and inequivalve shell, 

 but distinguished by a notch on the side of this ligament for the passage of a 

 byssus. 



The most known species, Oslrea malleus, Lin., which ranks among the num- 

 ber of high-priced and rare shells, has the two ends of the hinge extended, 

 and forming something like the head of a hammer, of which the valves, 

 elongated in a transverse direction, represent the handle. It inhabits the 

 Archipelago of India. 



VULSELLA, Lamarck, 



A little salient plate inside of the hinge of each side, from one of wlu'ch to 

 the other extends the ligament, otherwise similar to that of the Ostrese. By 

 the side of this plate is a notch for the byssus, as in the Mallei. The shell is 

 elongated in a direction perpendicular to the hinge. 



The most known species inhabit the Indian Ocean. 



PERNA, Bruguieres. 



Several parallel cavities across the hinge, opposed to each other in the two 

 valves, and lodging as many elastic ligaments ; the irregular and foliaceous 

 shell marked on the anterior side and under the hinge by a notch traversed by 

 the byssus. The Pernse were also left by Linnaeus among the Ostrete. This 

 genus is now subdivided. 



In the second subdivision of the Ostracea, as well as in almost all the 

 bivalves which follow, besides the single transverse muscular mass of the 

 preceding genera, there is a fasciculus which is placed before the mouth, 

 and extends from one valve to the other. It is apparently in this subdivision 

 that we must place the 



ETHERIA, Lamarck. 



Large inequivalve shells, as irregular as those of the Ostrese, and more so ; 

 no teeth to the hinge ; the ligament partly external and partly internal. They 

 differ from theOstreae in having two muscular impressions. The animal is not 

 seen to produce a byssus. 



They have lately been discovered in the Upper Nile. 



AVICULA, Bruguieres. 



An equivalve shell with a rectilinear hinge, frequently extended into wings 

 by its extremities, furnished with a narrow and elongated ligament, and some- 

 times with small notches near the mouth of the animal ; in the anterior side, 

 a little beneath the angle of the side of the mouth, is a notch for the byssus. 

 The anterior transverse muscle is excessively small. 



Mytilut margaritifenu, Lin., has nearly a semicircular shell, greenish 

 without, and ornamented with the most beautiful nacre within. The latter is 



