Miscellaneous. 511 



just published in the * Philosophical Transactions,' affords two in- 

 stances of a similar character, where shells of very much the same 

 external appearance — so much so that he regarded them as varieties 

 of the same species — proved to contain animals of a very different 

 organization, showing that they were the shells of very distinct spe- 

 cies of Mollusca, — as, for example, Lingula Anatina (t. 64) and Lin- 

 gula affinis (t. (jQ), and the two shells which he describes as Wald- 

 heimia australis (t. 52. f. 1) and W. australis, var. (t. 52. f. 3). 



These examples, showing that the animals, which are very alike in 

 external appearance, and even having the same shell, are distinct 

 when their internal structure is anatomically examined, — and that 

 shells, which are so much alike that they would only be regarded as 

 varieties of the same kind, have animals with very different organic 

 characters when they are more minutely compared, — should, I think, 

 make us much more careful than we have been in deciding what are 

 and what are not distinct species, from the comparison of the shell 

 alone, and especially where we have only fossil specimens in a more 

 or less imperfect state to compare with recent ones, or vice versd. 



It is for this reason that I have been disinclined to regard the 

 species of Crepidula, found in so many and such distant stations, as 

 the same species, though they may have the same external form, and 

 may offer the same varieties when found under similar circumstances, 

 as on the outside or inside of shells, or when clustered on each 

 other. 



I am for the same reason inclined to doubt whether the polypidoms 

 of different Zoophytes or Polyzoa really belong to the same species 

 of animal, though no external difference can be discovered between 

 the polypidoms of specimens brought from very different and distant 

 stations. If this be the case with living species, which are sent to 

 us in a comparatively perfect state, how much more reason for caution 

 when we are comparing fossil with recent specimens, or fossil speci- 

 mens with each other ! 



Saxicava a Byssus-spinner, By F. H. West, Esq. 



On the 14th of April, I placed a full-sized specimen of Saxicava 

 rugosa in my tank, where it remained for more than a fortnight, 

 lying helplessly on its back, but evidently healthy, and during the 

 latter part of the time having the foot pretty constantly protruded. 

 I then made a rude hole in a piece of old wood, and placed the Saxi- 

 cava in it, with the ventral surface downwards, in the hope that it 

 might excavate a more suitable dwelling for itself. In the course of 

 the following week, I examined it and removed it from the cavity, 

 but saw nothing of consequence. Two days later, however, though 

 the creature did not seem to have burrowed any further into the 

 wood, it was firmly fixed in its burrow, though hoWj did not appear. 

 On the 1 2th of May I cut away the wood very carefully from the 

 under side as far as the point of attachment, and found, as I sus- 

 pected, that the Saxicava had fixed itself by a true byssus to the 



