328 Dr. Maton's Desa^iption of 



of Mya variabilis is the radiating ruga, or plaits, Avhich proceed 

 from the apex of the nmboncs, and cover nearly the whole of the 

 shell. This circumstance, added to some others, induced me, at 

 first, to look upon this shell as a variety of Mt/a corrugata, of 

 Miiller [Hist. Verm. ttrr. etfiuv. 2. p. 214. n. 398), but, on con- 

 sulting the figures of that species given in the Beschaft des Gesell. 

 Naturf. Fremide zu Berlin, (torn. 4. p. 35. tab. 3. f. ?• 8), and by 

 Schrbter {Flussconch. n. 182. tab. 9- f- 3), I at length decided to 

 the contrary, its habit being totally different, though, from the 

 ambiguity of the description given iu Gmelin, I might have 

 made a very gross mistake, had I been unable to consult the au- 

 thors just mentioned. In fig. 6 of the plate annexed to this 

 paper, it Avill be seen that the ritgce, though so strong over the 

 whole of the younger shell (fig. 5), are very indistinct as they 

 pass towards the margin, and in fig. 4, the oldest of the three 

 specimens, they are almost obsolete, except on the decorticated 

 umbo : it will be remarked also, that the outline of the shell be- 

 comes totally different at its full growth, gradually verging from 

 a subrhomboidal, or somewhat obliquely oval, to a subrhombic 

 or almost orbicular form. As these differences are so marked, no 

 person, I conceive, who duly considers the facts which I have 

 mentioned, will be liable to separate Mya variabilis into several 

 species. 



3. Tellina limosa. 



Tab. XXIV. Fig. 8, 9, 10. 



Tellina testa aequivalvi, ovata, transversim striata, intus pur- 

 purea, umbonibus acutiusculis prominentibus. 



Habitat in America australi, fiuviatilis. 



Testa vix fragilis, glabra, epidermide viridi, margine integro, 

 ^ pollicis longa, i pollicis lata. 



Fig. 10. 



