CONCHOLOGY. 



racy of scientific discrimination may demand *, it is heterogeneous, and 

 unnatural, and in the aggregated form in which his annotator Gmelin 

 has left the genus, in the last edition of Sijstema Natures it is still tnore 

 exceptionable. He allows of no distinction founded on the character 

 of the animal inhabitant beyond its being a nereis, a molluscous animal, 

 or worm, defined as having a ringent mouth and two thicker tenta- 

 cula behind. But to those who have an opportunity of examining 

 those various animals that are thus designated in general terms, the 

 Nereides, it must be obvious, that however obscure their characters' 

 they are materially distinct : the investigation of them is unquestion- 

 ably attended with difficulties, but those difficulties are not insur- 

 mountable. The solitary Sabellse such as our present species, and the 

 Sabell« that associate together in masses as the Sabella alveolata, 

 present an obvious difference in the structure of their habitations; 

 and the animal has been also found to possess characters that remove 

 them yet further from the solitary Sabellse. Considerable caution is 

 also requisite in the examination of the Gmelinian Sabellae, lest we 

 include the larvae of certain insects that reside in the fresh waters, 

 and, of which the Ephemerae are definitive examples ; some of those 

 inhabit an elongated, or cylindrical case, or covering composed of 

 sandy particles and other adventitious matter ; the fragments of 

 aquatic shells, or the smaller shells entire, and others again the twigs 

 or stems of aquatic plants and fragments of reeds, and even grass. 

 And there is some reason to apprehend that a few of those supposed 

 fresh water Sabellas already described may hereafter prove to be in 

 reality no other than the larvae of the Ephemerae, Phryganeae, 

 and other similar tribes of insects, that usually reside in watery places. 

 The definitions of Lamarck are more explicit ; the true Sabella?, or 

 in other words, the animals of this kind that inhabit the marine 



