254 TRANSACTIONS OF THE WAGNER FREE 



Subgenus Turbonilla s. s. 



The genus Turbonilla was founded by Risso (using a manuscript name of 

 Leach) on three fossil species, two of which according to his figures were 

 polished, transversely ribbed, with no tooth on the pillar and with no spiral 

 sculpture. The third was similar, but had a fairly distinct plait on the pillar. 

 In his supplement he added a T. Humboldti, a recent species which appears to 

 be an Odontostomia. The synonymy of the group, which has been excess- 

 ively subdivided, is so profuse and complicated that the writer will not 

 attempt on this occasion to apportion it. The endeavor to identify the fossil 

 specimens and compare them with an extremely large series of recent forms, 

 comprising about a thousand individuals from the American coast and four or 

 five times as many from the coasts of Europe, has convinced the writer that 

 these small shells are extremely variable in several characters which have 

 often been relied on for separating them, even into subgenera as well as 

 species, and that the group cannot properly be divided on the basis of the 

 tooth or plait on the pillar or its absence. The transition from a straight 

 pillar to one slightly twisted, and from a slight twist to a stronger one, be- 

 coming in sturdy individuals a well-marked plait, is extremely gradual and 

 sometimes traceable in individuals of the same speties. Doubtless there are 

 species which always have the pillar straight and devoid of a plait. But there 

 are others, so closely related to them as to be hardly distinguishable, which 

 have a faint plait, or none, indifferently ; and occasional individuals of these 

 have a strong plait. The plait is frequently invisible from the aperture, but 

 sharp and strong in the whorls half way up the spire, where by cutting away 

 the wall of the whorl it may be seen. The attempt to transfer all the plaited 

 species to Odontostomia has been a failure, and many of them will have to 

 re-enter this genus when better known. For the present it will be more pru- 

 dent to group both toothed and simple species under the subgenus as re- 

 stricted. The following scheme will be convenient for assorting the .species : 



A. Shell without spiral sculpture ( Turbonilla s. s.). 



a. Ribs ceasing abruptly at the periphery ; 



a* pillar straight, simple ; 

 «t pillar twisted or plaited. 



b. Ribs becoming gradually obsolete on the base ; 



A* pillar straight, simple ; 

 if pillar twisted or plaited. 



B. Shell sculptured axially and spirally. 



a. Ribs ceasing abruptly at the periphery ; 



a* pillar straight, simple ; 

 a\ pillar twisted or plaited. 



b. Ribs gradually obsolescent ; 



b''' pillar simple ; 



b\ pillar twisted or plaited. 



C. Shell sculptured spirally or smooth. 



c* pillar simple ; 

 c\ pillar twisted. 



