460 NOTES AND MEMORANDA. 



One dorsal tooth only was present, in 



Two dorsal teetli only were 



Three 



Four „ 



Five 



Six „ 



Seven „ 



Ventral teetli were absent in 



One ventral tooth present in 



Two ventral teeth „ 



Three „ „ 



The range of variation being so considerable, it is evidently un- 

 profitable to compare this race with the published accounts, which 

 are based on examination o£ ten or a dozen specimens of other 

 races. Such a comparison will therefore be deferred until it is 

 possible to obtain an extended sei-ies of observations, from which a 

 fuller knowledge of the diagnostic characters and range of variation 

 of the species may be obtained. 



The development of Palsemonetes has been shown by P. Mayer,'^ 

 Boas,-j- and others to present a series of interesting variations. The 

 races which inhabit those countries surrounding the Mediterranean 

 — and which ai*e found almost exclusively in fresh water — exhibit, 

 as is well known, a more abbreviated development than the races 

 of Northern Europe, which inhabit exclusively waters containing 

 at least some admixture of salt. 



It is curious that the attempt to grow the southern forms in salt 

 water has not been successful. 



In June last several gravid females were taken from the stream 

 at Saltram, whose specific gravity was then 1*010, and placed in an 

 aquarium in the Laboratory at Plymouth. The density of the water 

 was diminished l3y< 0*001 daily, so that in ten days it became quite 

 fresh. The adult individuals fed freely, and seemed in no way dis- 

 turbed by the change of density, while the eggs hatched in due 

 course. 



The larvae at hatching were about 4 mm. long- ; the rostrum was 

 in some cases, though not in others, provided with a single basal 

 spine. 



The inner ramus of the second antenna was unsegmented. The 

 mandible was provided with biting teeth, but was not bifid. The 

 exopodite of the second maxilla was large ; and the four endites (of 

 which the distal was divided) were provided with well-developed 



* Mitth. Zool. Sta. Neap., Bd. ii, p. 196. 



f Spengel's Zoologisclie Jahrbiiclier, iv, p. 793. 



