SPINNING MOLLUSCS. 291 



habits of these latter creatures — terrestrial, fresh-water, and 

 marine univalves, and Sea-Slugs.* 



PULMONATA. 



In Pulmonata, other than Land-Slugs, spinning chiefly occurs 

 among the air-breathing fresh-water Snails, in which it is pro- 

 bably general. Among the Land-Snails of the order it appears 

 to be very rare ; the Helicidce (typical Snails) are entirely un- 

 represented, as also, with the exception of a single genus, are all 

 the other groups with Helicoid shells. For Pupidce we have two 

 notes, but these, as it appears to the writer, are in need of con- 

 firmation. With regard to the more or less Helicoid, semi-Slug- 

 like Vitrina pellucida, one finds that Mr. Collinge several times 

 tried, without success, to induce the creature to suspend itself ; t 

 and a few trials by the writer with various land-shells (which were 

 placed on twigs of needle-furze, &c.) were also unsuccessful, the 

 animals gliding off and falling without a thread, or retiring into 

 their shells and remaining on the twigs. In Testacellidce, I tried 

 Testacella scutulum ; in Vitrinidce, Vitrina pellucida ; in Helicidce, 

 young Helix aspersa and nemoralis (or hortensis) ; in Pupidce, 

 Clausilia laminata and G. rolphii ; and in Stenogyridce, Cochlicopa 

 lubrica, 



Zonitid;e. 



According to Andrew Garrett, the mucus of Trochonanina 

 conula,t and of other species of Trochonanina, is unusually 

 tenacious, *' and the animals possess the habit of ' thread-spin- 

 ning ' to perfection " ; so much so, it is added, that it requires no 

 small amount of patience, while gathering specimens, to detach 

 them from the fingers, and secure them in the box or vial.§ 



* On the subject of the mucus-threads of Land- Slugs, I hope to give, in 

 another place, details of observations and references ; in addition to these 

 molluscs, and to those now considered, the Mollusca-Pelecypoda (bivalves) 

 are thread-makers and by ssus- spinners, but I am unable at present to write 

 of the habits of this class of Mollusca. For help in preparing the present 

 paper, and in other tasks, I am much indebted to the courteous and continued 

 co-operation of my friend Mr. G. K. Gude. 



f Collinge, Zool. (3), xiv. (1890), p. 468. 



I Microcystis conula. 



§ Garrett, ' Journal of the Academy of Natural Sciences of Philadelphia ' 

 (2), viii. (1881), pp. 383-4 ; ix. (1884), p. 21. 



x2 



