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It has not hitherto been doubted that Salm. bicolor and rarispina were two 

 good species. Especially in Döderlein's most excellent work a full description is 

 given of both of them, and the distinctive features are pointed out. S. rarispina is 

 distinguished from S. bicolor „durch die kleinen, sehr weit von einander entfernten 

 Hauptwarzen der Apicalseite, durch die auffallend flache Unterseite und das kleine 

 Buccalfeld, durch die sehr spärliche Warzenbildung, welche die Obertläche auf- 

 fallend nackt erscheinen lässt, sowie durch die rautenförmigen Zeichnungen auf der 

 Schale". (Op. cit. p. 721.) According to the description of the species given by 

 DÖDERLEiN there is, however,- a great variation in all these features; only in the 

 character of the flat actinal side in S. rarispina no variation is mentioned, but as 

 DÖDERLEIN had only two specimens of rarispina for examination, much stress can- 



not be laid on this fact — and from my rich material it is seen that no reliable 

 distinction can be found herein either. Also the height of the test is rather variable. 

 In a letter to me Doderlein has further pointed out that the number of coronal 

 plates is distinctly smaller in rarispina than in bicolor. This will not always hold 

 good either. When comparing the measurements of S. bicolor cited above from Döder- 

 lein (p. 720) with the measurements of my Siamese specimens, it will be seen that the 

 specimens from Mauritius agree with the Siamese form in the number of the coronal 

 plates. There are then only left the two specimens from Ceylon and the one of 

 unknown locality. Among the Siamese specimens there are none of 62 mm. diameter, 

 so that only the specimens of 40 and of 565 mm. can be directly compared with 

 specimens oi rarispina. We have then in a specimen of 40 mm.: 40 ambulacral and 



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