183 



Possessing only one specimen, which can fairly be referred to the 

 stones here treated of, my inquiries respecting them are not likely to 

 be so successful as I could wish. In this specimen alone, however, I 

 am convinced, that I have discovered marks sufficiently strong to 

 prove, that the coat by which these entrochi are united, was ex- 

 tended over them during the life of the animal, to produce some effect 

 essential to its ceconomy. 



One of these entrochi (a) passes upwards in a straight line, and is 

 nearly surrounded by a spiral turn of the second (b) ; both being 

 nearly invested by a superinduced spathose matter, marked by two 

 seams running in the line of contact of the two entrochi. 



In the lower and fore part of this specimen the twisted column 

 is less thickly covered by this additional matter, and the straight 

 column is quite free from it, for a small space. It is to the exar 

 mination, which is thus fortunately admitted, of this small part, that 

 I am indebted for the ability to add one more conjecture, as to the 

 nature and use of this substance by which the two series of trochitre 

 are united together. Part of the trochitae of the straight column are 

 thus brought to view ; and these are, at first sight, seen to differ in their 

 colour from trochitae in general : the discolouration being very diffe- 

 rent from that which is found to proceed from different impregna- 

 tions of a mineral nature. The colour which is here observable is a, 

 livid grey, such as would not demand any long consideration in one 

 accustomed to see diseased bone, to induce him to suspect, from the 

 colour alone, that these parts had been under the influence of disease. 

 Being thus impressed by this appearance, I anxiously sought for evi- 

 dence which might determine how ill or well this suspicion was 

 founded ; and therefore proceeded to make inquiry, whether such con- 

 comitant circumstances existed here, as might be expected, if any 

 analogy existed between the effects of the assumed disease of these 

 parts and those which are known to accompany the disease of the 

 bone. 



