170 Memoirs of the Indian Museum,. [Vol. VII, 



porting to be an abbreviated reference to the earliest work in which a particular 

 specific name has received a definite meaning. If, however, the author quoted is one 

 who has only given an ambiguous definition, the abbreviated reference fulfils no 

 useful purpose. To be historically and scientifically useful, the reference should be 

 to the earliest author who has bestowed a definite meaning upon the name, whether 

 or not it may previously have been used in an unsatisfactory manner. For instance, 

 ' Dolium, maculatum, Lamarck" does not convey any useful information since it is 

 not possible, from Lamarck's description, to ascertain which shell he had in view, 

 while "Dolium maculatum, Deshayes " immediately gives the required clue since we 

 need only refer to Deshaye's work to know precisely which form is meant. 



Characteristic differences between the two species. — From the foregoing description, 

 it is clear that the forms under consideration are both very well defined and remark- 

 ably constant, and it is easy therefore to detect the particular features that differen- 

 tiate them from one another. Amongst the more striking differences, the following 

 may be particularly mentioned. 



Firstly. The protoconch in Dolium tessellatum is smaller, more prominent, less 

 oblique, darker-coloured than in Dolium maculatum. The secondary infilling of 

 porcellaneous shell-substance which occupies the whole interior of the protoconch in 

 the case of Dolium maculatum does not reach the apex in the case of Dolium 

 tessellatum. 



Secondly. The number of primary ribs visible on the spire-whorls is three or four 

 in the case of Dolium tessellatum, two or three in the case of Dolium maculatum. 

 The intervening spaces in the case of Dolium maculatum carry intercalary threads of 

 three orders, of which only those of the highest order are apt to disappear with 

 increasing growth. In the case of Dolium tessellatum the intervals, in the portion 

 immediately following the protoconch, carry intercalary threads of two orders only, 

 all of which vanish entirely or almost entirely with increasing growth. 



Thirdly. The number of primary ribs on the body-whorl of Dolium maculatum 



is ten or eleven, and remains perfectly constant at all stages of growth. In the 



case of Dolium tessellatum the body-whorl of very small specimens carries twelve 



primary ribs, the number increasing, by anterior additions, to as many as sixteen in 



the case of very large specimens. 



Fourthly. The intercalary decoration in the case of specimens of average size of 

 Dolium maculatum includes, in the broader intervals, threads of two orders, much 

 narrower than the primary threads. In the case of very large specimens some of 

 these intercalary threads may broaden into bands resembling the primary ribs, while 

 threads of a higher order may also appear. In the vast majority of specimens of 

 Dolium tessellatum there is practically no intercalary spiral sculpture on the body- 

 whorl. In the case of very large specimens there may appear some intercalary 

 bands, the number of which, in a single primary interval, never exceeds two. These 

 intercalary ribs of full-grown specimens of Dolium tessellatum are apt to assume the 

 maculated colour decoration of the primary ribs, while this is very rarely observed 

 in the case of Dolium maculatum. 



