98 PROCEEDINGS OF SOCIETIES. 



naturally, on the appearance of stormy weather, retreat from the surface, by ex- 

 hausting the float, and remain at the bottom until the gale had subsided. 



A very interesting paper on the lanthina, from the pen of that talented natu- 

 ralist, Mr. William Clark, of Bath, is published in the " Annals of Natural 

 History" (January, 1853), and, as it contains much valuable information, I claim 

 permission to make the following extract : " This genus has long caused embar- 

 rassment to naturalists, and is still a source of difficulty in regard to the structure 

 of the animal and its natural position ; but I think the obstacles to a true determi- 

 nation will disappear on attentive consideration. The great stumbling-block is the 

 float, as it is called, or vesicular mass, attached to the foot, which has been con- 

 sidered an hydrostatic apparatus. This idea is erroneous. The organ is the mem- 

 braneous vehicle of the contents of the ovarium and matrix that has descended from 

 under the mantle, and fixed itself to the foot, for a very obvious purpose of the 

 animal economy, in reference to the pulli in the genial season. It is probable, 

 that as the animal, from its peculiar habitat, cannot, like the tribes of the coasts, 

 deposit the germs of reproduction on marine substances, it makes use of the foot as 

 a substitute, until its young emerge from the agglomerated mass of capsules to 

 shift for themselves, and then the temporary vesicular deposit is cast off. I have 

 seen a similar appendage to the foot of the Pileopsis hungaricus and several other 

 gasteropoda. That this organ is not necessary for the floatation of the animal is 

 strongly supported by the fact, as the sexes are distinct, that many may be presumed 

 the males, and such often occur without the so-called float. Many of the Littorinse, 

 with a shell ten times more ponderous in proportion than the globular, delicate 

 lanthina, float, with the shell beneath and foot uppermost, in every direction, for 

 days, without descending from the surface of the waters." 



I would now beg to observe, that I cannot make all my specimens agree with 

 the description given by Forbes and Hanley, who say of this shell " the suture is 

 distinct, but simple, and never canaliculated ;" and I have the pleasure of laying 

 before you a series exactly answering to this description. 1 have also selected 

 another, in all of which, from the young up to the adult, the suture is strongly 

 marked, and, I think, I should be justified in stating that it is slightly canalicu- 

 lated. In addition to this, as far as I have observed, the shell grows "to a larger 

 size, is heavier, more spiral, the whorls more globose, and it is often more closely 

 striated. I beg to lay this series also before you, in order that you may judge of 

 the correctness of my observations. I would suggest, though with much diffidence, 

 that there are sufficient distinguishing characteristics in this second series of lan- 

 thinse to entitle them to be made, at least, a variety of the species communis. 



I had written thus far, when I was much gratified by accidentally finding that 

 my views though not, as I imagined, original agreed with those adopted by 

 Forbes and Hanley, in the appendix to their work on the British mollusca, as in 

 this they figure an lanthina closely approximating to those in my second series, 

 respecting which they write, that "until the genus lanthina shall have experienced 

 a thorough revision, and the effect of local circumstances in producing variation of 

 colouring, chasing, and contour upon its migratory members shall have been duly 

 estimated, it will be hazardous to define the limits of the several varieties or species 

 which, by the past generation of conch ologists, were included in the Helix janthina 

 by the present, in the I. fragilis or communis. Krauss, in his useful work on 

 the Testacea of Southern Africa, remarks, " that the indigenous shell, figured by 

 Chemnitz, is very different from the Neapolitan one, termed bicolor by Philippi, 

 though both are usually cited as identical. Our British examples, again, seem 

 different from either, and were considered so by Dr. Leach, who, we are informed 

 by Mr. Jeffreys, termed them Britannica." Referring to this plate, which, I might 

 mention, is taken from an Irish example, they say " that it differs from those 

 previously described in so many particulars, that it becomes of importance to spe- 

 cify them." But I will not introduce that description here, as I have not given a 

 detailed one of that which I consider to be truly entitled to the specific name of 

 fragilis. It is only just for me to mention, that they, in conclusion, express some 

 doubts as to its being admitted as a distinct species, inasmuch as they remark, that 

 " a more than ordinary latitude seems permitted to shape in this species, because 

 the larger turns do not always strictly coil in a regular spiral, but, sometimes de- 



