!•_> THE VOYAGE OF H.M.S. CHALLENGER. 



mandible with six teeth, Darwin, however, one with five teeth and an inferior point, which 

 in tins species is rather broad and finely pectinated. To show the correctness of my 

 interpretation one has only to compare the figure of the mandible of Lepas anatifera in 

 Darwin's Monograph (Lepadidse, pi. x. fig. 5) with his description: "mandibles with, as 

 usual, five teeth," &c. ; moreover, when giving this description, Darwin refers to the figure 

 in pi. x. According to Darwin, the maxillae have four regular steps; according to v. 

 Willemoes Suhm, they have sometimes four, and more commonly only three steps, besides 

 the two large unequal upper spines. This difference does really exist, at least if Darwin's 

 description is correct. I always observed only three steps, both in the maxilla of the 

 Clialleno-er specimens, from which PL I. fig. 6 is drawn, and also in the maxillse of one of 

 the specimens collected by the Brothers Krause in the neighbourhood of the Tschuktschen- 

 Peninsula. 1 Von Willemoes Suhm, however, did not always observe the same number, and 

 this shows clearly, I believe, that the importance of this difference is not very great. In 

 the descriptions of the different species of the genus Lepas, Darwin, moreover, has given 

 numerous instances of variations in the number of teeth, both in the mandible and in the 

 maxilla. There is another point, however, which at first made me think it necessary 

 also to consider this Pacific form as a distinct variety of the Atlantic one. This is the 

 smoothness, when seen with the naked eye, of the chitinous membrane which covers 

 the valves and fills out the interspaces between them. According to Darwin, this 

 membrane is thickly clothed, especially in the interspaces between the two valves, with 

 minute spines, barely visible to the naked eye. As I said above, the Pacific specimens, 

 when seen with the naked eye, do not show a trace of spines, and only a certain roughness 

 may be distinguished, which is occasioned — as an investigation with the microscope 

 brings to light — by extremely thin and flat threads, which often seem to adhere to the 

 chitinous membrane at more than one point. Often also numerous microscopic Alga? are 

 present at the surface, and contribute not inconsiderably to this roughness. The specimens 

 from the northern coast of Siberia, collected by the Brothers Krause, show exactly the same 

 condition of the surface as the Challenger specimens. 2 In all other regards the Pacific 

 specimens agree entirely with Darwin's description, except in so far as the size is concerned. 

 And this is perhaps the most considerable point of difference between the Pacific and the 

 Atlantic form. The size of the capitulum of the largest specimen does not quite reach 

 25 mm., whereas the Atlantic specimens often have a length of 40 mm. The large 

 Atlantic specimens, though brittle, have a shell considerably stronger and more calcareous 

 than the smaller specimens. 



In the Pacific Ocean about 100 specimens (and often a much more considerable 



1 These specimens belong to the Natural History Museum of Bremen. The} 7 were kindly sent me for examina- 

 tion by the Director of the Museum, Dr. Spengel. 



2 In the Atlantic specimens this roughness is not the rule ; of late I have been enabled to study specimens 

 from Vineyard-Sound (United States of America), and these show exactly the same condition of the surface as thi se 

 of the Pacific. 



