116 Mr, R. M'Andrew on the Comparative Size of MuUusca 



growu from their short, thick, Dendritine type; and also of that 

 peculiar variety of Vertebralina striata in which the later cham- 

 bers curve round and embrace the earlier spiral portion {Renu- 

 lites opercularis) ; nor is the mode of growth essentially different 

 in Orbiculina, which shows this tendency in O. adunca and its 

 varieties, and becomes perfectly cyclical in some individuals, — ti 

 feature which is the typical character in Orbitolites. 



[To be continued.] 



XL — Note on the Comparative Size oj Marine MoUusca in various 

 Latitudes of the European Seas. By R. M'Andrew, F.R.S. 



In the ' Natural History of the Eui'opean Seas,' by the late 

 Prof. Edward Forbes, edited and continued by Mr. Godwin- 

 Austen, I meet with the following passage, treating of the 

 shells of Piedmont : — " ' It is remarkable,^ says Mr. Jeffreys, 

 ' that examples of the same species are smaller than those found 

 in the British seas : Tellina balaustina, Jeffrey sia diaphana, and 

 Rissoa pulcherrima are instances of this.^ The diminution in 

 size which is to be observed with respect to many other species, 

 such as Corbula nucleus, when traced from north to south, is the 

 moi'e remarkable because the converse does not take place as 

 to southern forms in their range north. Haliotis tuberculata, 

 which extends through the whole Lusitanian zone, is larger at 

 Guernsey, which is the extreme northern limit, than elsewhere. 

 Ringicula auricnlata and Mactra rugosa are larger in Vigo Bay 

 than in the Mediterranean, though at Vigo they are both out- 

 liers ; and Tellina balaustina, which has its numerical maximum 

 in the Mediterranean, is largest about the Hebrides." 



I do not question the correctness of Mr. Jeffreys^s remark 

 applied to the shells collected by him on the coast of Piedmont ; 

 but to infer from it, and from the other instances cited by 

 Mr. Austen, that jMollusca generally, or any large proportion of 

 them, whether belonging to northern or southern latitudes, 

 increase in size as they advance northward, and none in a 

 southerly direction, is a grave error, which I feel called upon to 

 dissipate, as far as this end can be accomplished, by a statement 

 of the results of my own experience bearing uj)on the point ; 

 because, in order to advance our knowledge, I look upon it 

 as more essential to get rid of existing fallacies than even to 

 establish new facts. 



Corbula. nucleus diminishes in size when traced northward 

 as well as southward from the British seas, and is as large 

 at Lisbon, or even at Malaga, as upon the shores of North 

 Drontheim. 



