ZS8, 



I 



PLEUROTOMA, 



TESTA fusiformis, turrita, apertura ovali, ca- 

 nali plus minusve elongata, labio externo prope 

 sutiiram emarginato; opentulo corneo, infra 

 acuminato, nucleo inferiore. 



An interesting Genus of elegantly fusiform univalves, 

 separated from the Linnean Murices. The spire being in 

 general much elongated and gradually tapering to a line 

 point; and a more or less elongated straight canal bring it 

 near to Fusus, from which it is Only distinguished by the 

 notch in the upper part of the outer lip. To Murex, as 

 we have already defined that Genus, it does not appear to 

 be nearly related. Notwithstanding that in general the 

 form of the Pleurotomce is such as we have described it, 

 there appears to us to be several variations of form brought 

 together under this generic appellation ; we think, however, 

 that they cannot be separated. One of these variations 

 of form is an approximation to Strombus, having a short 

 canal and the outer lip somewhat expanded, some of these 

 have also a notch near the lower part of the outer lip; 

 another is an approach to the cones, having a very nearly 

 straight columella and a linear aperture. Two genera, 

 namely Pleurotoma and Ctavatida were formed in 1801 by 

 Lamarck to contain the shells which he has since united 

 together in Pleurotoma, the one having been distinguished 

 from the other principally by the shortness of the canal, 

 some of the species which he then named Clavatula are, 

 however, very peculiar and might perhaps without im- 

 propriety be separated from Pleurotoma. Upon glancing 

 over our collection of Pleurotoma? we observe several 

 variations in form which it may not be amiss briefly to 

 describe, they are as follows : Jirst, with the spire and the 

 canal nearly of equal length, a single keel near the middle 

 of each volution, and a deep notch in the outer lip imme- 

 diately helow the keel, such are PI. Babylonica, P. Virgo 

 and others; second^ with the canal rather shorter than the 

 spire, a nodular keel near the middle of each volution 

 and a deep notch in the outer lip above the keel, PI. Java- 

 nica and nodifera are examples of this form ; third, with 



