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nigricans is rather easily recognized, as the light is seen through 
the leaf when kept against the window. 
Åvr., longicaulis is the most common species of the Avrainvil- 
leas in the Danish West Indies, where it occurs in deeper water at 
a depth of about 20—30 meters. 
It has been found hitherto: at St. Thomas in the sea west 
Fig. 2. AÅvrainvillea nigricans Decaisne. 
Compare text. a,b about 7”; c about 79/;, 
of Water Island; St. Jan in the sound between St. Thomas and 
St. Jan off Christiansfort, and near the Gt. St. James Isle. 
This species has already been found at St. Thomas by the 
Challenger-Expedition; Murray and Boodle have called it Avr. 
longicaulis (Murray and Boodle Il. c. p. 70). At my request Mr. Gepp 
has kindly examined the specimen to be found in the British Museum 
and writes to me as follow: "The St. Thomas '"Challenger” speci- 
