GASTEROPODES. 289 



4. TRITONIA CONIFERA The Pine Tritonia. Plate XLI. Figs. 12, 13. 



I have sometimes conjectured that the subject of this paragraph 

 might be a lusus natures ; but not being entitled, without better evidence, 

 to presume that it is so, a place is reserved for it here. 



Length five lines ; general form and aspect resembling the Tritonia 

 pinnatifida ; tentacula two, long, retractile, within dilatable sockets ; a 

 dark speck is obscurely seen, behind the root of each, by the microscope. 



Six pair of branchiae : two, being a pair of stumps, rise from the 

 back. The first pair is very low, the second disproportionately large, the 

 third pair not half their length or thickness, the fourth and fifth dimi- 

 nishing, and the stumps denoting incipient organization. Besides all 

 these, a large central branchial tuft or cluster is situate on the back, 

 between the two branchiae of the third pair. The structure of the tufts 

 bears some resemblance to a pine-apple, the prominences somewhat higher 

 comparatively. Colour of the animal dingy white, the tufts darkly 

 speckled. 



The motion of this animal, when crawling, appeared unsteady, from 

 the disproportion between the size of the tufts and of the body. Under 

 the microscope the latter resembled ovoidal prominences ; the central 

 one, at the summit, larger than the rest. Five series, or stages, compose 

 the tuft. 



Only one specimen of this animal occurred, which survived nine 

 weeks. 



PLATE XLI. 



FIG. 12. Tritonia coni/era. 

 13. A tuft, magnified. 



Note. A species, somewhat analogous in the formation of the 

 branchiae, is referred to in the Melibcea fragilis. Forbes' Malacologia 



Monensis, p. 41, Plate I, figs. 4, 5. 



2o 



