SouLEYET ^) regards tlie representatives of his genus Spirialis as being sirnpl)- Cleodora-ioxm?, 

 "dont la partie posterieurc du corps et de la coquille sont contournees en spirale", while 

 Grobben ^), who thinks that the ventral mantle-hole is the original one, attributes the dorsal 

 position to the twisting of the visceral mass, but calls the mantle-hole of the Cavolinidae 

 secondary-ventral. 



Boas ^) was the first who gave an explanation of the connection, mentioned above. 



He pointed out, how the Cavolinidae have proceeded from the Limacinidae by a turn 

 of 1 80° (in the opposite direction of the hands of a clock) of the hind part of the body, which 

 has stretched itself with respect to the head part, so that the latter (foot, fins, tentacles, penis, 

 etc. *) shows the greatest conformity in both the families. But the mantle-hole, the ending of 

 the intestinal canal, the heart, the efferent duct of the gonad, are differently situated in both 

 families in so far that the organs which are situated dorsally, ventrally, to the right, or to 

 the left in the Limacinidae, have their place just in the opposite direction in the Cavolinidae. 



Boas fully explained his assertion, so that I can refer to his work for further particulars. 

 Pelseneer ^) modified Boas' theory somewhat. According to him, it is not the hind part that 

 has made a turn of 180° with respect to the fore part (or vice versa), but both the parts have 

 turned 90° in different directions with respect to each other. This had to be proved by the 

 retractor muscle. According to Boas ^), part of this muscle, running to the right of the 

 oesophagus, is a new formation, while Pelseneer, referring to Fol "), just regards this branch 

 as beine the original, which also radiates in both the fins. 



At the same time Pelseneer showed the affinity between the Limacinidae and the 

 Cymbuliidae, which had not been discovered by any investigator before him. Here, too, the 

 revolving process of 180° has taken place. Though the full-grown animals of the Cymbuliidae 

 seem to show very little resemblance with the Limacinidae, yet there are a great many important 

 points of conformity with Peraclis in respect to the (left-handed) larvae of the first mentioned family. 



Family L Limacinidae. 



1847. Limacinidae Gray, the Genera of recent Mollusca, Proc. Zool. Soc. London, p. 203. 

 1853. Hyalidae (part.) d'Orbigny, in Ramon de la Sagra, Histoire physique, politique et 



naturelle de I'ile de Cuba, vol. I, p. 70. 

 1859. Spiralidae Chenu, Manual de Conchyliologie, vol. I, p. 113. 

 1863. Limacinacea Troschel, Das Gebiss der Schnecken, Bd. I, p. 50. 



The animals, representing this family, are nearly always very small. A dimension of a 

 few mm. may be called considerable already, and there are only two species which strike the 



1) SoULEYET. Voyage de la Bonite. Vol. II, p. 208 — 215. 



2) Harn- und Geschlechtsorgane der Cephalopoden. Arb. Zool. Inst, Wien. Tome 5, p. 63. 



3) Spolia Atlantica. p. 19 — 22. 



4) But not the central nervous system, as Boas says. 



5) Challenger Report. LXVI, p. 28 — 37. 



6) Spolia Atlantica. p. 22, note 1. 



7) Arch, de Zoologie. exp. 1875, Vol. IV. Sur le developpement des Pteropodes. pi. IV, fig. 43, 44. 

 SIBOGA-EXPEDITIE LII, 



