30O JOURNAL OF CONCHOI.OGY, VOL. 9, NO. 10, APRIL, 190O. 



So far, then, as the shell alone is specifically diagnostic, L. burnetii 

 is more worthy of separation than L. involuta. 



Jeffreys, 1 speaking of L. involuta, says : " It has some affinity to 

 Z. glutinosa, and may ultimately prove to be an aberrant form of 

 that species, corresponding with the variety burnetii of Z peregra. 

 Very little is known with respect to the external parts of the body ; 

 but Professor Goodsir has given some valuable details of its internal 

 organisation. He says: "In structure the Limnceus involutus re- 

 sembles the other species of the genus," from which remark it might 

 be inferred that the mantle has not the expanded lobe which is pecu- 

 liar to the sub-genus Amphipeplea. Dr. Perceval Wright, however, 

 informs me that " the greater part of the shell in this species is 

 covered by the mantle, as in Z. glutinosa." 



Mr. Stubbs and myself kept our captive specimens alive for a 

 couple of days, and watched them carefully, but we did not see a 

 trace of overlapping mantle ; and Mr. J. W. Taylor says : " I have 

 had L. involuta in confinement for some little time, and the mantle 

 never overspread the shell, though under close observation." I can 

 only conclude that Dr. Wright's information was incorrect. 



It was surprising to find so late as September ioth that none of the 

 examples were more than half grown, most being only a quarter of 

 their full size, seing that at this time of year L. peregra has usually 

 attained maturity. But what seemed more surprising was the quan- 

 tity of fresh-laid egg-masses attached to stones. L. peregra is about 

 the earliest breeder of the genus, commencing to pair with the first 

 encouragement of warm spring days ; nor does it pair after August — 

 rarely after July ; and though Moquin-Tandon says : (i Gamier 

 observed an isolated individual in a glass vase lay twenty-six times 

 from the ist July to September 24th," this was under artificial con- 

 ditions. But whether Z. involuta habitually postpones pairing till the 

 autumn I cannot say. In July, 1898, Messrs. Collier and Chaster 

 visited Loch Crincaum, but they did not find any egg-masses. I do 

 not think the altitude of the habitat (798 feet) can have anything to 

 do with the matter when the very mild climate of south-west Ireland 

 is considered, especially since at considerable elevations close by 

 Killarney Z. peregra was found normally forward. 



Mr. Madison informs me that " Z. burnetii was pairing in Loch 

 Skene on April 4th, 1S96, and began to deposit spawn during the 

 first week in May." The shape of the egg-masses of Z. involuta was 

 invariably spherical and not sausage-shaped, as are those of L. peregra. 

 Mr. Madison says " I do not think there is any difference in the eggs 

 of Z. burnetii and Z. peregra." 



1 Brit. Conch., vol. i, p. 103. 



