Mr. W. Clark on the Chemnitzise. Ill 



T l j, diameter y 1 ^ uncise. This description will be the sequence of 

 my account of the shell in a former Number of the ' Annals of 

 Natural History/ 



A second example has shown, that the transverse groove in 

 the foot does not exist, and that in the first specimen it was 

 due to contraction, which when it is completely developed dis- 

 appears ; nevertheless the structure is peculiar : at rest it is sub- 

 oval, but divided into two portions by an apparent superficial 

 line due to colour ; when fully deployed, the anterior one is con- 

 stricted, slender, attenuated, capable of great extension, slightly 

 auricled and emarginate, subhyaline white ; the posterior portion 

 is suboval, short, broad, fleshy, of an opake pale drab, divided by 

 a deep medial longitudinal fissure, that seems almost to penetrate 

 the integuments into two lobes, forming together a rounded 

 termination with a narrow central emargination. 



Chemnitzia decussata, Montagu. 



Animal inhabiting a pale drab spiral decussated shell of 4-5 

 volutions ; it is hyaline white, except the proboscidal muzzle, that 

 passes for the mentum with some malacologists, which is pale 

 pink or red. The mantle is even. The muzzle of this species is 

 less lobed and more truncate than in its congeners, but it has 

 at times varying phases ; it is small, subcylindrical and narrow, 

 and on the march, as is the invariable practice in all the species, 

 it is in advance of the anterior portion of the foot, which, like 

 the terminus of the rostrum, is truncate and without the auri- 

 cular points at the angles ; it is rather broad, and when extended 

 reaches halfway on the antepenultimate volution, posteriorly be- 

 coming a little constricted, and has a very rounded termination. 

 The tentacula are triangular, bevelled laterally, pointed, with the 

 usual two minute flake-white lobes at the tips, which may be 

 partly real, but principally simulations that depend on the will 

 of the animal ; the lateral membranes, which are not so extensive 

 as in some species, coalesce and form a shallow veil ; the eyes 

 are very close together strictly at the internal bases, not im- 

 mersed, but are a little elevated on minute prominences. We 

 may remark, that in this tribe the membranes on both sides of 

 each tentaculum simulate all kinds of shapes and foldings, which 

 have been termed auriform or subtubular ; these are deceptions, 

 and due to the will of the animal, as on the march the tentacula 

 are always carried in a regular, smooth, triangular, bevelled po- 

 sition ; these changes from one form to another only occur when 

 the animal is disquieted by position ; then they are frequently 

 and suddenly made, and as quickly assume a natural form. The 

 operculum is of a narrow, rather elongated oval shape, carried on 

 a simple lobe at some little distance from the posterior terminus 

 of the foot ; it has the usual characteristic right-angled semi- 



