344 DR. GWYN JEFFREYS ON THE MOLLUSCA OF THE [May 20, 



original. Upwards of forty years ago the late Edward Forbes pro- 

 posed to distinguish species in the same way. But it is notorious that 

 the relative value and constancy of these characters have yet to be 

 determined, and that there is no standard of reference by which natu- 

 ralists can be guided in adjudging some forms to be species and others 

 to be varieties in different genera. Every naturalist, whether of the 

 old or the "new" school, must form his own opinion. I have already, 

 in the first chapter of the introduction to my work on 'British Cou- 

 chology' (pp. 18-19, 23), fully stated my views on this difficult 

 and hitherto unsettled question. 



In the present species the apical whorls are pinched up and nar- 

 rower than the rest of the spire ; the mouth in perfect specimens 

 resembles that of Pherusa gulsonce. 



L- 4. AcLis VENTROSA, Jeffreys. 



A. ventrosa (Jeffr.), Friele, Bidrag til Vestlandets Molluskfauna 

 (Vid. Forh. 1875, separate copy), p. 5, t. i. f. 7, 7a, 7h. 



'Porcupine' Exp. 1869: St. 23a. 1870: Atl. 16. 



Distribution. Lofoten I. {G. O. Sars), Bergen {Friele) ; 200- 

 300 fms. 



More conical and broader at the base, and with the whorls more 

 rapidly increasing, than A. walleri. It belongs to the genus Hemi- 

 aclis of G. O. Sars. 



^ Pherusa gulson^, Clark. 



Chemnitzia gulsonce, Clark in Ann. & Mag. Nat. Hist. 3rd ser. vi. 

 p. 459. 



Aclis gulsonce, B. C. iv. p. 106 ; v. p. 210, pi. Ixxii. f. 5. 



'Porcupine' Exp. 1870 : Atl. St. 27, 28. Fragments only. 



Distributio7i. British and Irish coasts from Shetland to Guernsey, 

 Vigo Bay {Mc Andrew), Palermo (Monterosaio), Madeira ( Watson) ; 

 20-103 fms. 



Fossil. Pliocene; Coralline Crag, Sutton (S. Wood). 



See ' British Conchology ' for the description of the animal and 

 shell, which shows the peculiar characters of this moUusk. I had 

 there suggested the generic name Menippe ; but as that name had 

 been previously employed in the Crustacea, I venture to substitute 

 Pherusa, which was at one time given to it by Mr. Clark, the 

 discoverer of the shell. I cannot explain the meaning of this name. 



Family XVII. PyramidellidjE. 



Apex having a sinistrorsal and exposed spire. 



It is unnecessary, if not a waste of time, to recapitulate the facts 

 and arguments which I used in 'British Conchology' (vol. iv. pp. 

 108-111) for the purpose of proving that the subdivision of Odo- 

 stomia into several genera is really unscientific, and is not based on a 

 single valid character. The presence of a "tooth" or columellar 

 fold, the length of the spire, and the kind of sculpture (if any) are so 

 variable, that it is quite impossible to distinguish or separate certain 



