SEA-FISHERIES LABORATORY. 385 



" The first, which belongs to Arctic waters, is thick- 

 " walled and gross, and is the true R. hebetata. The 

 " second, R. semispina, has thinner walls and is pro- 

 " portionately longer, and it is furnished with a long 

 " hair-like point at each end. Its distribution extends 

 " over practically the whole Atlantic, though it is chiefly 

 " to be found in the neighbourhood of the cold currents. 

 " These two ' species ' can originate from one another 

 "reciprocally as the result of one cell-division. During 

 " the course of transition a cell may be hebetata at one 

 " end and semispina at the other." This is just what 

 we find is happening with our Biddulphia sinensis. 



Biddulphia mobiliensis (Bailey), as figured by 

 Ostenfeld in the volume of the " Internationale Revue " 

 referred to above, is not nearly so common in the Irish 

 Sea as the larger form he names B. regia (Schultze), 

 and which we have all along recorded as Biddulphia 

 mobiliensis (see figs. 16-19). We now regard it as 

 probable that these three so-called species are all forms of 

 the same Diatom in various stages of transition or modi- 

 fication. Bailey's name, mobiliensis , appears to be the 

 older one, and ought to be adopted in preference to the 

 others. For the sake of uniformity with the records in 

 our previous reports, we continue to use the names 

 sinensis and mobiliensis for the two forms shown in 

 text-fig. 3 (p. 381), although we are not now inclined to 

 regard them as being distinct species. They are, we 

 consider, two forms (B. mobiliensis, forma sinensis, and 

 B. mobiliensis, forma regia) of the original species 

 B. mobiliensis , Bailey. 



On the other hand, however, we are informed by 

 Dr. E. J. Allen that he and Mr. Nelson succeeded at 

 Plymouth in growing pure cultures of the forms 

 Biddulphia sinensis, B. mobiliensis and B. regia* and 



