335 



between the extremes regarding the whole genus as an enormous 

 protean species, or describing nearly every colony as a separate 

 species. Here characters can be seen varying in all directions, 

 and in almost all degrees, though some variations seem to be 

 fixed, whilst others remain indefinite. This is very perplexing 

 in the definition of species, though to the student of evolution 

 this difiiculty will be full of interest. 



►Specimens presenting a sinus in the outer lip are too rare (and 

 so far only observed in two species) to use this feature in the 

 arrangement of the species, but the form of curvature, which 

 the incremental lines present, may prove of importance ; the 

 exigencies of publication have, however, prevented me testing 

 fully the classificatory value of this character. 



The internal septation, which is exhibited by two of our 

 species (T. septifragn, in which it is invariable and frequent, and 

 T. tristira, observed in one instance), is a feature hitherto unre- 

 corded in the genus. 



SYNOPSIS OF SPECIES. 



Whorls smooth, or not distinctly lirate, subimbricating. 

 ►Shell very elongate, posterior whorls medially carinate. 



1. sejjtifraya. 

 Shell under 15 mm., anterior whorls ridged posteriorly. 



2. pagodula. 

 Whorls carinate and lirate. 



Keels granulose. 



Keels three, median granulose. 3. Aiding ae. 



Keels three, anterior and median granulose. 



4. Warhurtoni. 



Keels three, middle one granulose. 5. Sturtii. 



Keels four to five, all granulose. 6. gemimdata. 

 Keels not granulose. 



Keels three, equal. 7. tristira. 



Keel one, very prominent. 8. conspicabilis. 



Keels two, whorls imbricate. 9. acricida. 

 Whorls lirate. 



Lirse numerous, sijuamose, whorls medially concave. 



1 0. Murray ana. 

 Line under 20, more or less une(|ual, whorls flat f)r imbricate ; 



shell slender. 9. acricida. 



Liras five or less, whorls flat or slightly convex. 



1 1 . jjlatyspira. 



SPECIES EXCLUDED. 



Turritella transenna, Tenison- Woods, Proc. Lin. Soc, vol. TTL, 

 p. 234, an Eocene-fossil at JNIuddy Creek, is transferred to 

 MathUda. 



