No. XI.— ON THE CEPHALOPODA OBTAINED BY THE PERCY SLADEN 

 TRUST EXPEDITION TO THE INDIAN OCEAN IN 1905. 



By G. C. Robson, B.A. 



(Published by permission of the Trustees of the British Museum.) 



(Communicated by Prof. J. Stanley Gardiner, M.A., F.R.S., F.L.S.) 



(Plates 65, 66, Text-figs. 1—6.) 



Read 17th June, 1915. 



An examination of the Cephalopoda obtained by the " Sealark " on her cruise in the 

 western regions of the Indian Ocean has been delayed since the return of the expedition 

 in 1905 until the beginning of'the present year [1914] when Prof. Gardiner placed them 

 in the author's hands. 



The collection consists of eighteen species representing ten genera and includes a 

 new genus and two new species. Although no very remarkable forms were obtained, 

 the collection as a whole is not without interest, while some of the anatomical features 

 revealed by dissection are of importance. 



A peculiar feature of this collection is the total absence of Myopsida {Loligo, Sepia, 

 etc.). This group usually being of a littoral habitat their absence in conjunction with 

 the relatively large number of pelagic and abyssal forms might be taken to shew that 

 the "Sealark's" work was confined to deep-sea dredging or tow-netting far from land. 

 This however was not the case. As will be seen from a study of the stations from 

 which the various species were obtained some of the Polypods were taken at very 

 moderate depths off the islands at which the "Sealark" touched: so that the absence 

 of Myopsida is difficult to account for. 



In the present state of our knowledge of the group. Cephalopoda are a rather 

 unprofitable class for use in zoogeographical studies. Those that are well known (the 

 Polypods, squids and cuttlefish) have usually a very extensive range (or what appears to 

 be so), being for the most part powerful swimmers. For example, Polypus fontanianus 

 ranges from Chili to the Indian Ocean ; while Stenoteuthis bartramii is cosmopolitan. The 

 delicate abyssal forms, on the other hand, are so little known at present that it would be 

 useless to generalize on their distribution. 



We have also to bear in mind the fact that the diagnoses of a great many species 

 of Cephalopoda are based upon external characters of doubtful value, and that a different 

 view of their distribution may be taken when students of this group have paid more 

 attention to the description of internal parts. Distributionar areas at present ranging 

 over many degrees of latitude and longitude may by this process become more restricted. 

 The habits of the majority of these animals, however, do not leave much ground for 

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