42 N. ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. VI. PROSOBRANCHIA. 2 SEMIPROBOSCIDTFERA. 



nuniber of wliorls, it is suitable to proceed intlie same manner as was described for Natica 

 clausa (page 21), that is, to state the number for small specimens and from these calculate 

 that for the larger ones. Thus, the foUowing survey is obtaiiied showing the connec- 

 tioii between whorls and size for L. tenuistriata of different districts: 



Numbor of whorls: 



II e i g h t of t 11 e s h e 1 1 

 from 



Mossel Bay 



Advent Bfiy 



Iceland 



Miitotselikin Sliar . . . . 

 Behring Sound and Sea . 



2 7. 



3'/, 



4'/, 



5 



15 





iwh.47,:13.7) 



23 



13 



20 



(wh. 47,-. 12.5) 



20 



about 17 



24 



5 72 



1.9 



about 2,5 



(\vh. 2^1, : 3.7) 



4.7 



about 4 



3.6 



4 

 about 5 



about 5.5 



(wh. 3^, : 8) 



5.5 



abovit 5.5 



7 



11 



9.5 



9 



8—9 



about 12 



(wh.5'/,:31) 

 2G.5 



From these numbers it is evident that the increase of size is somewhat retarded on 

 Iceland and Matotschkin Shar, but here the shells, by way of compensation, are thicker 

 and more ponderons. 



Tariatioii of the Rartula. 



The median tooth has a strong central cnsp and 2 lateral ones, wliich are some- 

 what more prominent than in L. pallida. The lateral teeth ha ve strong denticles, 1 — 3 

 on the outer side of the primary ciisp and a few others on its inner side. The inner un- 

 cini are bicnspidate and the onter cusp is usnally the largest (in L. pallida the cnsps are 

 equally strong but sometimes the inner one may be larger). The form of the teeth varies 

 somewhat — thus specimens from Matotschkin Shar and Advent Bay ha ve a very broad 

 median tooth with a large crown, the breadth being about twice the length; in E. Green- 

 land tliis tooth is somewhat narrower. 



General Remarks. 



L. tenuistriata, though a quite distinct species, wliich exhibits a seemingly constant 

 character even in the colouration of the animal, has by most authors been confused with 

 L. pallida. It was first described by Searles Wood (1848) as Natica groenlandica Beck 

 and figured by him (T. XII, Figs. 5 a, b). From the descrif)tion and the figure it is ob- 

 vious that his specimen from the Bridlington Pleistocene is a form of L. tenuistriata, 

 which appears to be most like the recent Iceland specimens, Mr. F. W. Harmer, the 

 celebrated English geologist, who has kindly made a comparison between Wood's original 

 specimen and one shell from the Ice Fiord, is also of the opinion that the two shells 

 are identical. 



Bulbus Smithii of Brown (1838) may perhaps be identical with the present shell 

 and not with Acrybia flava Gould. The figure and the description given by Brown 

 (pag. 104) seem to be applicable to L. tenuistriata, above all the words »aperture some- 

 what semi-lunar or oblong-ovate, straitened and pointed above and expanding widely 



