46 JOURNAL OF CONCHOLOGY, VOL. 10, NO. 2, APRIL, I9OI. 



POLYPLACOPHORA. 

 Tonicia atrata Sow. {=Chiton atrahis'^oy^., Mag. Nat. Hist., N.s., 

 vol. 4, 1840, p. 294). — Many examples of a very rare species, which 

 has hardly been collected since the time the original specimens came 

 to hand. The markings are exceedingly variable, as is the colora- 

 tion, some being cinereous, others warm fawn or umber; others, 

 again, mottled with light and dark hues. Some, too, are beautifully 

 lineated with white or pale-grey. In all our examples, however, there 

 is one uniform point of similarity, viz., the pale stramineous girdle, 

 which is perfectly smooth and plane. 



Tonicia lebruni Rochebrune. — A single example of a rare 

 species, described by M. de Rochebrune so recently as 1884. 



Callochiton iiluminatus Rve. (= Clu'fon illuminatus Rve., 

 Conch. Icon., t. 22, fig. 147, 1847). 



Plaxiphora setigera King. — Two specimens. 



PELECYPODA. 



Mytilus edulis L. — "Very numerous. On the morning of Nov. 

 29th, 1898, a specimen placed in a pan of sea-water the day previous 

 was found to have spawned. During the afternoon of the same day 

 a number of mussels were detected in the act of spawning in several 

 places in the harbour, the sea being calm, and the sun shining 

 brightly at the time. Towards the end of the following month, when 

 the tow-net could be used, their larvje formed one of the commonest 

 objects in the gatherings. By the 21st of January, 1899, these larvae 

 had settled down to various objects in the harbour, and it was noticed 

 that while they seemed to avoid the kelp {Macrocystis), other marine 

 weeds, Hydroids, Ascidians, and in fact everything available was simply 

 covered with them. Soon after arriving at Stanley it was noticed that 

 many of the beds of mussels, more especially in the neighbourhood of 

 Whale Sound, contained a large percentage of dead shells, with the 

 valves still united by the ligament. Enquiry elicited the fact that the 

 previous winter had been one of exceptional severity, and doubtless 

 the depopulation of these large areas was owing to this cause, the 

 mussels having been frozen when uncovered at low water. Mac- 

 gillivray^ records a similar destruction of the mussel beds in Stanley 

 Harbour. In many parts of the harbour the shells of this species, and 

 also those of Patella, seem subject to erosion or decay in the shell 

 substance ; perforations appear, and the mollusc soon succumbs. 

 Only specimens living on the shore are thus attacked, those on hulks 

 and stone walls escaping. The disease is probably due to the rain- 



I " Narrative of the Voyage of H.M.S, ' Rattlesnake.' " vol. 2, p. loo, 



