Stridulation in Crustacea Decapoda. I. 59 



front margin. When the chehpeds are moved forwards and 

 backwards a moderatel}' strong sound is produced. 



(More than fort^^ years ago Wood-Mason pointed out a 

 special feature in another species of the genus Ovalipes {Platyo- 

 nichus), viz. 0. bipustulatus M.-'Edw., and interpreted it as a 

 stridulating organ. The lower surface of both chelse have a good 

 number of transverse, serrated ridges, but these are not fully 

 as regular as usual in a stridulating organ, and I have been un- 

 able to point out with certainty any part which can act as bow ; 

 in this case observation of living animals are necessary for 

 settling the question.) 



2. Acanthocarpus Alexandri Stimps. — Both chelae are 

 similar; each is large, ver}' high, with the inner side somewhat 

 flat ; on this smooth surface is seen a somewhat curved, vertical, 

 distinctly raised area somewhat before the insertion of the 

 movable finger. The area reaches about to the upper margin of 

 the chela and occupies scarcely three-fourths of its height; its 

 upper half is somewhat broad, but it tapers rapidly above and 

 slowly from the middle downwards; the area is adorned with a 

 high number of very fine and very closely set ridges which are 

 ver\' obhque on the long median line of the area, and the ridges 

 are equally close in its whole length. On the lower side of the 

 orbit and further outwards somewhat below and a little behind 

 the front margin of the carapace runs an oblique, thick keel, 

 which is broadest at its middle, narrower towards both ends 

 and especially outwards ; each keel has 8 or 9 transverse, rounded, 

 rather thick ridges arranged v^ry regularly, and each interval 

 is about twice as broad as one of the ridges. When the chela is 

 moved forwards-upwards and in the opposite direction below 

 the front part of the carapace, it is rubbed against the ridged 

 keel described, and produces a rather high sound. — This 

 species has been taken in West Indies and somewhat more 

 northwards in depths from 71 to 150 fath. ; one of the 



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/:st, 





