UNIVALVES. 



PLATE LIV. 



Genus. MUREX, &c. 



The following Plate is intended more particularly to point out the natural dis- 

 tinctions of the genus Murex, when compared with the Pyrula and Pleurotoma; 

 for this purpose, and to make the difference of their form more obvious, five curious 

 shells of opposite shapes are herewith represented, and which may tend to make 

 the system by which they are divided, much more intelligible. 



Species. 



No. 1. Pyrula undulata. Shell of a pale red, marked transversely with wavy 

 sutures ; mouth slightly marked with flutes, and the spire rounded and fur- 

 rowed. Native place unknown. 



No. 2. Murex rubicunda. Shell of a dark red; the mouth broad, angular; co- 

 lumella slightly fluted; spire angulated and tuberculous. 



No. 3. Murex lineata. Shell brown, marked all over with a band consisting of 

 two lines similar to threads ; the spire angular and tuberculous ; the mouth 

 broad and angular, of a square shape. A native of the West Indies. From 

 the Author's Museum. 



No. 4. Pyrula Australasia. Shell of an olive green ; the mouth of a dark brown, 

 rounded ; spire rounded, streaked within. A native of New Holland and 

 Van Diemen's Land. 



No. 5. Pleurotoma acuta. Shell of a white colour, spotted with square marks ; 

 the spire divided into hollow channels ; the cheek of the mouth having a 

 projecting swelling and cavity, which forms the distinguishing character of 

 the Pleurotoma, and by which it differs essentially from the Murex. 



REMARKS. 



There is no doubt, that upon a transitory view of the shells described in the above Plate, 

 the general resemblance in their forms appears so striking, as almost to lead to a supposition 

 that they are of one genus, which circumstance, however, is to be explained only in the fol- 

 lowing manner. The Murex genus has a pointed and rocky appearance in the form of the 

 body and spire; the Pyrula, on the contrary, has a rounded body and spire, and ending also 

 in a more circular termination. Of the peculiarities of the Pleurotoma, perhaps sufficient 

 remarks have already been made in the description of that curious genus, and which the 

 present comparison of forms may serve in some degree farther to elucidate. 



