CHAP. VII. TROCHID.E. TURBID^. 



ANALOGIES. 



223 



geological beds, which we only know from casts and 

 mutilated fragments ! and how many others, even in 

 the newer formations, which it is impossible to arrange 

 with precision, from ignorance of the animal ! These are 

 the true reasons which lead us to say as little as pos- 

 sible upon all those fossil genera whose affinities are 

 doubtful ; since, from the peculiar nature of the object 

 we have in view, we would rather incur the imputation 

 of overstrained caution, than the opposite extreme. 



(208.) We have hitherto considered only the affini- 

 ties of the TrochidcB ; let us now turn to their analogies. 

 Our first table will be of the primary divisions, or sub- 

 families, which represent those of the Turh'idcR in the 

 following manner : — 



Analogies of the Sub-families of the Trochid^ and the 



Turbid^. 



Sub-families of 



TrockidiZ. 

 Typical Genera. 



Senectus. 



Trochus. 



ROTELLA. 



Pleurotomaria. 

 Phasianella. 



Analogical Characters. 



c (1. Sub-typical.) 



•J Shell globose ; operculum shelly 

 c spire short, obtuse, ventricose 

 (2. Typical.) 

 Spire pointed; whorls more nu- 

 merous ; operculum horny. 

 (3. Aberrant.) 

 Shell depressed ; inner lip thick 

 ened. 



C Trochiform ; the outer lip with a 

 X marginal slit or sinus. 



f Spire greatly lengthened 

 X culum shelly. 



Sub-families of the 



Turbidai. 



Typical Genera. 



Ampillaria. 



\ 



\ 



Melania. 3 



Thallicera. 



Ianthina. 



^ ^' i TURRITELLA. 



Whatever may be the rank of Pleurotomaria, it is 

 certainly the prototype of Ianthina. These latter shells 

 are so excessively brittle, that not one in five hundred 

 are perfect j but the sinus, although neither so long nor 

 so narrow as in Pleurotomaria, is nevertheless fully de- 

 veloped in the perfect shells, but more especially in our 

 /. gJohosa.* The long-spined Turritellce represent 

 Phasianella, and both have a shelly operculum. The 

 other analogies are not so striking,— excepting, perhaps. 



• Zool. 111. 1st Series. 



