340 GENUS LITKOTKYA. 



below the other, generally in a straight line, and are 

 attached firmly to one side of the burrow. The discs are 

 oval, or rounded, or irregular, and are commonly from 

 2*0 th to -roth of an inch across : they usually form a quite 

 straight ribbon, widening a little downwards : each little 

 disc overlaps and extends beyond the one last formed, 

 fully half its own diameter. I have seen one row of discs 

 an inch in length, but the upper discs are always worn 

 away by the friction of the calcified serrated scales on the 

 peduncle. It is very important to observe that the lowest 

 disc is not fixed, (as was the case with the cup,) at the very 

 bottom of the burrow, but on one side, just above the 

 bottom, which latter part is occupied by the blunt basal 

 end of the peduncle. 



In a valuable paper on L. Nicobarica, by Reinhardt, 

 presently to be referred to, the disc is said to be attached 

 on the carinal side (see fig. 2) of the peduncle ; and this, 

 I believe, is general. I have seen one instance in which, 

 during the excavation of a new burrow, an old burrow 

 was met with, and the row of discs turned down it, 

 making, with their previous course, nearly a right-angle. 

 In another similar instance, the discs, instead of turning 

 down, became very large and broad, and so fairly formed 

 a bridge across the old burrow (fig. 1), — becoming narrow 

 again as soon as the animal recommenced burrowing into 

 the solid rock. Sometimes, as it appears, the animal, 

 whilst still small, from some unknown cause, stops bur- 

 rowing downwards, and then a cup is formed at the bottom 

 of the hole. As soon as the animal has got to its full 

 depth, the burrow increases only in diameter, and during 

 this process the linear row of discs is ground away and 

 lost ; a cup is then formed. The little discs can be de- 

 posited or formed only at each fresh exuviation ; and as 

 some of the burrows are above two inches in depth, and 

 as on an average each disc does not extend beyond the 

 underlying disc more than Tsth of an inch, an animal 

 which has bored two inches in depth, must have moulted 

 at least thirty times. I may here remark that I have 



