308 Transactions of the Society. 



There are a few points, however, on which I would insist a 

 little more at length. The " wings," or peristoniial lobes, are in 

 our species very unequal in length, and Kent describes them as 

 such in the following terms : " Peristome lobes rounded, of unequal 

 size ; one of these, usually the left, attaining twice the dimensions 

 of the other." Does this inequality in length really concern now 

 one of the lobes, now the other, and more generally the left, as 

 Kent supposes ? Unfortunately my observations on the subject 

 have been very few and the results uncertain, owing to the 

 difficulty of deciding among the crossing lines ; but in my notes I 

 find four sketches in which the longer lobe seems to be the right, 

 and two where the left seems the longer. 



The study of the peristome is also rendered difficult by the very 

 variable aspect of the lobes ; they may be but incompletely 

 expanded, or one of them only attains its full length ; now they are 

 more or less retracted, and now so fully expanded that the border 

 falls back behind, etc. 



Very often one of the lobes, more generally the larger, does not 

 look rounded at the summit, but terminates in a sharp point 

 (figs. 2, 3), which results from the fact that F. holtoni — like 

 Wright's F. stylifera — is provided with a special appendage, a 

 median crest which runs along the dorsal surface of the lobe, and 

 is extremely contractile. When the contracted animalcule begins 

 expanding, this special appendage is always in an advanced 

 position (fig. 8), as if exploring the vicinity. When the lobe is 

 fully expanded, the appendage usually disappears, though frequently 

 leaving, just behind the summit of the lobe, a faint knob. Very 

 often, however, it remains a long time in sight, like a triangle 

 crowning the summit of the expanded lobe (fig. 3). 



This special appendage seems at first sight to belong only to 

 the larger lobe, but the smaller one is in fact provided with it, and 

 sometimes shows a very distinct prolongation. In one specimen, 

 for instance, where the neck of the shell had been accidentally 

 compressed and did not allow of any expansion outside, but where 



DESCEIPTION OF PLATE I. 

 Folliculina boltoni. 



Fig. 1. — Animal expanded ; tlie shell (somewhat abnormal) seen nearly from 



the side. 

 „ 2. — One of the lobes of the peristome, seen from the side, with the protractile 



appendage at the top. 

 „ 3. — One of the lobes seen from the front, with the triangular protractile 



appendage. 

 „ 4. — An individual in its shell, expanded. 

 ,, 5. — Another, seen from the side, but the shell seen from the front (owing to 



some contortion of the animal). 

 ,, 6. — The shell seen from the side. 

 ,, 7. — An expanded individual, found free from its shell. 



