44 



The true limpets — Patella — have the gills disposed in a 

 circle round the mantle, in the space between it and the foot. 

 On detaching a limpet from the rock and placing it upon its 

 back in the water the mantle will be seen to spread out, dis- 

 closing the feathery filaments of the gills like a fringe round 

 the upper part and below the silvery muscular attachments. 

 Within this circle is the broad foot attached all round in its 

 upper part by the silvery muscles aforesaid, except an open 

 clear space for the free movement of the head, having a 

 rather large chamber behind in which is the excretory orifice. 

 The mantle is, however, continued round the shell in front of 

 the head, and in one of the Tasmanian true limpets so are 

 the gills. 



But in some limpets there are no gills round the mantle. 

 In this case, in one genus, they are placed at the back of the 

 head, and can be seen as a long feathery plume, coming forth 

 from the head chamber. This is the second genus AcmcBa, 

 I do not know of any difference by which the shells of the 

 genus may be distinguished. True limpets are sometimes 

 nacreous, Acmcsa, are never so. We have only two species of 

 true limpets in Tasmania certainly ascertained, while we have 

 many of AcmoBa. There are, of course, other limpets described, 

 but the animals have not been examined, and until they are 

 the shells must be considered as only provisionally classed. 



Besides the above arrangement of the gills we have limpets 

 which have no gills at all, but breath by a true lung. These 

 are the Siphonariae. Their anatomy is not well understood, 

 but what little is known removes them in their whole orga- 

 nisation very far in the animal rank from true limpets. As I 

 have had facilities for the examination of two of the species, 

 I have preferred to place my observations in this paper ; they 

 are not Patellidse, however. Their shells are only in some 

 slight details to be distinguished from limpets, which shows 

 us how little a shell of such simple character can be a guide 

 to the knowledge of the animal it shelters. 



In addition to the breathing apparatus we have in all 

 moUusca a very valuable organ as a means of identification, if 

 BOt of true classification. That is the lingual ribbon. It is a 

 long horny membrane, studded with minute points or teeth 

 of a very hard siliceous nature, sometimes vitreous and 

 transparent, but in all the limpets of a rich golden or dark 

 brown color. By some writers this organ is called a tongue, by 

 others teeth, radula, &c. For convenience I shall adopt a name 

 proposed by many naturalists, viz., odontophore. Its nature 

 and ofi5.ce are not thoroughly understood. I here record my ob- 

 servations in the case of the Tasmanian limpets. All of these 

 animals have strong cartilagenous jaws curved and swollen on 



