ASTARTE. 317 



It is not less variable than A. sulcata ; and if a spe- 

 cimen of the smooth, flat and triangular form were 

 placed side by side with the fine-ribbed, convex and 

 rounded variety globosd, it would be difficult to imagine 

 that they were the same species. A. compressa, in all 

 its phases, may be known from any of the smooth-edged 

 varieties of A. sulcata by its inferior size, the shape 

 being always more triangular than square, the beaks 

 being more central, and by the ribs (where they exist) 

 being much finer and more numerous in proportion to 

 the size of the shell. I received from Mr. Dawson of 

 Cruden a specimen found by him in the Moray Firth, 

 which had the hinge reversed, the right valve exhibiting 

 the teeth that properly belonged to the left valve, and 

 vice versa. The muscular impressions were as usual ; 

 but that would be the case, whether the right valve 

 had changed place with the left or they had retained 

 their normal relation to each other. I am not aware of 

 a similar instance of such a partial transposition. The 

 instances of Lucina Childreni and Chama Lazarus, men- 

 tioned by Gray in the ' Zoological Journal 9 and ' Philo- 

 sophical Transactions/ are different, inasmuch as those 

 shells are inequivalve. Bivalve mollusca can never be 

 completely reversed like univalves, because the internal 

 organs of the former are symmetrical, and those of the 

 latter are confined to one side or position. 



I have before observed that this is not the Venus 

 compressa of Linne. Among the many synonyms of 

 our species may be mentioned V. Montacuti, Turton, 

 Nicania Banksii, Leach, Crassina convexiuscula and 

 C. obliqua, Brown, A. multicostata and A. Uddevallensis, 

 J. Smith, A. pulchellaj Jonas, and A.propinqua, Lands- 

 borough. 



