144 



SOME REMARKS ON THE DETERMINATION OF 

 GENERA AND SPECIES. 



(Presidential Address delivered at the Annual Meeting, Oct. 15, igio). 



By Lt.-Col. GODWIN-AUSTEN, F.R.S. 



The few remarks I have to make this evenuig are the outcome of 

 some work I have been engaged upon during the last few months. 

 Those wlio have worked much at the land mollusca know how diffi- 

 cult it is to deal with certain species when locating them in generic 

 position. This is particularly the case with a type of shell more or 

 less thin and delicate, of few whorls, these rapidly increasing in size, 

 of subdued tint, and often shiny and polished. Such shells come 

 from all parts of the world, and Vitriiia pellucida may be taken as 

 the type of the form. The earlier conchologists (and it is not so many 

 years ago) placed all shells partaking in any degree of this shape in 

 the genus Vitrina, and it is often done up to the present time. Even 

 shells much more heliciform found their way into Vltrina — and at 

 that period no deductions of any value on distribution or relationship 

 were possible in this particular group of shells. 



It was not long, however, before the great difference was noticed 

 in the external form of the animals of true palsearctic Vitrina and the 

 Asiatic and tropical species, and a large number became transferred to 

 Helicarion, and other genera sprang into existence. Helicat-ioTi is, 

 even up to the present day, the happy resting place of all sorts and 

 kinds of land shells which happen to be thin and globose and with 

 no definite shell characteristics. 



Fortunately, although shell character is unsatisfactory, in the ex- 

 ternal structure of the animals and internal anatomy there are many 

 very clearly discernible characters which make comparison much 

 more easy, rendering generic and specific determination more satis- 

 factory. Trusting it will not weary you, I will mention a few which 

 can be observed. 



First, the external. I will not occupy time by referring to all these, 

 but refer to one which has been of help to me. On removing the 

 animal from the shell, there is the visceral sac. From the mantle 

 zone the wall of the branchial cavity, and the vicinity of the heart 

 and kidney is often beautifully mottled or streaked ; the patterns are 

 most varied, in one or more colours, in round spots or streaks ; and 

 although they are not absolutely identical in every specimen, yet on 



