322 PLIOCENE MOLLUSCA. 



1915. Alectrion (Tritia) trivittata, Johnson, Bost. Soc. Nat. Hist., Occ. Papers, vol. vii ; Fauna of 

 New England, no. 13, p. 135. 



Specific Characters. — Shell rather thin, ovato-conical, turreted ; whorls 7 or 8, 

 but slightly convex, with a narrow and square shoulder above ; spire regularly 

 diminishing upwards to a sharp and pointed apex ; ornamented by strong, equal 

 and equidistant spiral ridges, 4 on the upper ones and 10 on the body- whorl, inter- 

 sected by numerous fine costse which produce distinct granulation at the points of 

 contact; mouth oval, notched at the upper angle; outer lip thin, grooved within 

 by the spiral ridges; inner lip forming a thin glaze on the columella ; canal short, 

 notched, rather wide, turning to the left with a distinct groove at the back. 



Dimensions.— L. 15 mm. B. 8 mm. 



Distribution. — Recent : eastern coasts of North America. 

 Fossil : Pleistocene deposits, Macclesfield. 

 Plioceue : Iceland — Husavik. 



Remarks. — There is a fossil in the British Museum from the Macclesfield drift 

 which has been there identified with the recent New England species N. trivittata, 

 Say. It corresponds very closely with an example of the latter I have received 

 from Mr. C. W. Johnson of the Boston Society of Natural History. I have figured 

 these side by side with some specimens of N. propinqua from the Oakley Crag to 

 show wherein they agree and wherein they differ. The two forms are not the same 

 but they belong to the same group ; whether they should be regarded as specifically 

 distinct has been and probably will continue to be a matter of opinion. On the 

 whole it seems most convenient to retain the American name of N. trivittata for the 

 one which is a recent and, as now ascertained, a Pliocene Icelandic, as well as a 

 Pleistocene form, N. propinqua being reserved for the extinct and Pliocene shell of 

 the Anglo-Belgian basin. It is interesting, however, to find this link between the 

 molluscan faunas of the two continents. Possibly the newer is a modified descendant 

 of the older shell. 



By H. and A. Adams this American species was referred to the sub-genus 

 Tritia, of Risso (= Hinia, Leach), a view which has been recently adopted by 

 Mr. C. W. Johnson of the Boston Society of Natural History. 



N. trivittata was recognized by Wood among some fossils collected by Mr. J. 

 Starkie Gardner from the Icelandic Crag of Husavik. 



Nassa (Hinia) propinqua (J. Sowerby). Plate XXXIV, figs. 18, 19. 

 1914. Nassa propinqua, F. W. Harmer, Plioc. Moll. Gt. Brit., pt. i, p. 73. 



Remarhs. — For reasons just given I now propose to regard this shell as specifi- 

 cally distinct from the American N. trivittata, to which, however, it is closely allied. 

 As a Pliocene fossil it is only known from the Anglo-Belgian region, being very 



