14 

 A n a t o m i c a 1 R e m a r k s. 



Our knowledge about the anatomy of the genus Liinacina being considerably enriched by 

 Pelsexeer's researches '), I have scarcely anything to add to what has been published by this 

 able investigator. As he has done, so have I studied Lbiiacina helicina (from Matotschkin Strait). 

 The shell, the fins of the anima! , its radula and jaws have been figured by Sars ") (radula also 

 by BoAs)^), the tentacles and the whole visceral anatomy have accurately been described by 

 Pelseneer, to whose figures I can moreover refer *). 



The chief point is the fact, that the shell is sinistral (ultra-dextral), while the anima! 

 exhibits a right-handed organisation. 



The gonad consists of very numerous small follicles, occupying the whole initial portion 

 of the visceral mass. The penis includes a rounded horn piece, as in all "Pteropoda". — On 

 the left side of the stomach I have found a gastric caecum, which is perhaps the same as the 

 "bile duet", mentioned by Pelseneer (PI. I, fig. 2). 



The central nervous system is asymmetrical, the right portion of the visceral mass 

 being larger than the left. Pelseneer was the first who discovered this asymmetry, not only 

 in this case, but in all the genera of the Thecosomata. 



The supra-oesophageal commissure is attached to the median side of the right cerebral 

 ganglion (Pl. I, fig. 3 C). 



Though I have often sought for the second pedal commissure, I have not found it. 

 Only once I could see a small nerve (?) parting from the front of one of the pedal ganglia 

 and directed towards the other, but even in this case I have not been able to decide whether 

 this was a real commissure, or perhaps onh- a part of the very thin connective layer on 

 the ganglia. 



The otocysts are easily visible, owing to a brown pigment at the margins. 



As to the nerves which part from the central nervous system I noted two nerves 

 proceeding from the anterior part of the cerebral ganglia (not one, as Pelseneer has figured)"). 

 In any other respect 1 agree entirely with Pelseneer ; only the right pallial nerve was stronger 

 than the left (Pl. I, fig. 3 A, B, C). 



Auditory nerves I have not seen. 



Peraclis Forbes (emend.). 



1836. Heliconoides (part.) d'Orbigny, Voyage dans l'Amérique meridionale, vol. V, p. 174. 

 1840. Spirialis (part.) Eydoux et Souleyet, Description sommaire de plusieurs Ptéropodes 



nouveaux ou imparfaitement connus, Revue Zoölogique, vol. III, p. 235. 

 1844. Peraclc Forbes, Report on the MoUusca and Radiata of the Algean Sea, and on their 



distribution, considered as bearing on Geology, Rep. Brit. Ass. 1843, p. 186. 



1) Challengei' Rep. LXVI, p. 7 — 11. It must have been a lapsus cnlaiiil^ that the authov says (p. 7): "head distinct", this 

 being indistinct. 



2) MoUusca regionis arcticae Noivegiae, pl. 29, fig. I, pl XVI, fig. 17. Notwithstanding Sars deuies the existence of 

 jaws in Limacina^ saying (p. 328): "maxillae nuUae". 



3) Spolia atlantica, pl. III, fig. 22. 



4) Op. cit. Pl. I, figs. 1—8. 



5) Op. cit. s. Pl. 1, fig. 7. 



