16 



KR. BONNEVIE. 



[REP. OF THE "MICHAEL SARS" NORTH 



The shape of the m e d i a n teeth may in both species 

 vary somewhat with regard to the length of the spine, 

 but affords no absolute character of distinction. 



£.t 



^ t 



Fig. 13. Radula of Limacina retroversa. 

 l.t, lateral teeth; m.t. median teeth. 



The lateral teeth, however, are in fullgrown 

 specimens absolutely different with regard to the arran- 

 gement of their denticles, the denticled border of L. balea 

 (textfig. 14 B. 3) being in a very characteristic manner 

 divided into two halves, while in L. retroversa (textfig. 13) 

 no such division exist. 



The existence of such a distinctive character in the 

 radula, together with the statistical results as to the varia- 

 tions of the shell in the two forms, justify us in regarding 

 L. balea and L. retroversa as specifically distinct. 



Having compared the two species, I shall now treat 

 them seperately, trying to establish their relations to other 

 forms which have been referred to one or the 

 other. I am well aware that this task is one 

 of great difficulty, and that in some cases 

 only a detailed examination of the original 

 specimens can ensure an accurate deter- 

 mination. 



I have also endeavoured to gather trust- 

 worthy information about the geographical 

 distribution of the two species, and in doing 

 so have had to omit all data given by those 

 authors who consider L. retroversa and L. 

 balea as one and the same species. 



In order to give the reader an oppor- 

 tunity of testing the correctness of my opinion 

 with regard to the synonymy I have copied 

 a series of figures given by earlier authors 

 and grouped them according to their simi- 

 larity, paying special attention to the size 

 and shape of the body-whorl as compared 

 with the spire (textfig. 15 a— i and 17 a— dj. 

 The shape of the opening and the size of 

 the umbilicus are characters so relative, and 

 so inaccurately described by most authors, 

 that they can scarcely be taken into con- 

 sideration. 



Limacina retroversa Fleming. 



Heterofusus retroversus Fleming 1823, (p. 498, pi. 15. fig. 2). 



Atlante trochiforme d'Orbigny, 1836 (Moll. p. 177, pi. 12, fig. 29—31). 



Scaea stenogyra Phillipi, 1844 (p. 164, pi. 25, fig. 20). 



Fusus retroversus Jeffreys, 1847 fp. 16). 



Spinalis Flemingii Forbes & Hanley, 1850 (p. 382, pi. 57 fig. 4—5). 



Limacina retroversa Gray, 1850 (p. 33). 



— trochiformis Gray, 1850 (p. 33). 



Spiralis trochiformis Eydoux and Souleyet, 1852 (p. 223, pi. 13, 



fig. 27-34). 



retroversus (pars) Jeffreys, 1869 (p. 115, pi. 4, fig. 4). 

 Heterofusus retroversus Gould, 1870 (p. £05, pi. 27, fig. 345). 

 Spinalis retroversus Monterosato, 1875 (p. 49). 



G. O. Sars, 1878 (p. 330, pi. 29, fig. 3). 

 Limacina balea (pars) Boas 1886 (p. 43). 



— trochiformis Boas, 1886 (p. 45). 



Munthe; 1887 (p. 7, fig. 8—11). 



— australis Pelseneer, 1888 (p. 25, pi. 1, fig. 6). 



— trochiformis Pelseneer, 1888. 

 retroversa Locard, 1897 (p. 23). 

 balea (pars) Posselt, 1898 (p. 254). 

 trochiformis Oberwimmer, 1898 (p. 589). 

 retroversa (pars) Meisenheimer, 1905 (p. 419). 



1906. 

 balea (pars) Lenz, 1906 (p. 2). 



In textfig. 15 I have copied a series of drawings by 

 which some of the above named authors have illustrated 

 their species. As will be seen from the list of synonyms 

 I do not hesitate to identify L. trochiformis d'Orbig., with 

 L. retroversa, Fleming. Such an identification has been 



A 



/ 



B 



Fig. 14. Radula of Limacina balea: A of a young specimen, B of a full-grown 

 specimen; 1, 2 median teeth. 3, 4 lateral teeth. 



