TEREBRID^E. 5 



T. armillata and T. commaculata, seem to offer strong points of 

 difference, and good grounds for sectional heads. But, with every 

 wish to establish some such divisions, I have found it impracti- 

 cable so to group the species that there shall be little or no doubt 

 which section they belong to ; and unless this object is attained, 

 I do not see any use in a division ; science would not be bene- 

 fitted merety by selecting the salient points and strong grounds 

 of the exceptions, and leaving the crowd to follow as they may." 



H. and A. Adams, in their " Genera of Recent Mpllusca,' 1 

 include in the family Terebridse the two subfamilies Terebrinse 

 and Pusionellinae (the shells composing the latter are now con- 

 sidered a group of the family Pleurotomidae). 



They divide the subfamily Terebrinse into two genera : 



Acus, Humphrey. Animal with eyes on the tips of the ten- 

 tacles. Whorls without posterior band; aperture emarginate 

 anteriorly, not produced into a canal ; columella simple, incurved, 

 not tortuous ; outer lip simple, acute, without anterior sinus. 



A. maculata, Linn. 



TEREBRA, Adanson. Eyes at the outer bases of the tentacles. 

 Whorls with spiral groove forming a posterior band ; aperture 

 very small, canaliculated ; columella tortuous ; outer lip anteriorly 

 sinuous. T. babylonia, Lam. 



These characters of the shell shade off into each other by 

 gradual transitions, so that they afford no good grounds of divi- 

 sion, and the position of the eyes is at the tips of the tentacles 

 in all the species that have been examined. The eyes were 

 erroneously figured by Quoy and Gaimard, in T. subulata, at the 

 base of the tentacles, and this supposed peculiarity Messrs. 

 Adams have made one of the points of distinction between their 

 two genera. In the figure of the animal of T. subulata, in Gould's 

 Moll. U. S. Expl. Exped., the eyes are correctly placed. 



In the genus Acus, Messrs. Adams' have the following sub- 

 genera : 



ABRETFA, H. and A. Adams. Whorls longitudinally ribbed ; 

 columella simple, straight, produced. A. cerethina, Lam. 



HASTULA, H. and A. Adams. Whorls smooth; columella 

 simple, straight, produced anteriorly. A. albula, Menke. 



EURYTA, H. and A. Adams. Turreted, subfusiform, smooth ; 

 whorls nodosely plicate, the last rather ventricose ; columella 



