KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 99 



Local Distributiox.— The data for an adequate discussion of this phase of 

 distribution of these pelagic organisms is wliolly inadeqiiate for two reasons. 

 In the first place, there are no data from contiguous regions, and secondly, the 

 species herein discussed were progressively discovered and allocated, so that 

 within our own data the facts as to distribution are limited. 



It will appear to the reader of the systematic section of this work that very 

 few individuals have been seen of most of the species herein desci'ibed, whereas 

 the facts are that only those individuals are cited whose specific identity is 

 recorded in drawings or was determined and recorded during the searching of 

 the plankton. In the course of the investigation there were very many instances 

 of species not recorded or not run down on the slide until sufficiently quiescent 

 for certain identification. 



The individuals of many of the species are in fact much more abundant 

 than the data cited indicate. 



The following conclusions as to local distribution are based on our obser- 

 vation and records : (1 ) The species are very unequally represented in numbers. 

 Those which may be called conmion are relatively few. The folloAving were 

 common in the summer of 1917, or in previous years as noted, AmpMdinium 

 truncatum (191i) , Gymnodinium coeruleum (1906), G. costatum (1917) ; G. con- 

 tractum, G. dogieli, G. favmn (1914) ; G. gracile, G. hamulus (1914) ; G. Jietero- 

 striatum, G. lumda, G. ruhricaKda, G. rubrum, G. sphaencum, Gyrodiniimi 

 macidatum, G. ochraceum, G. pingue, G. ruhricaudatum, Cochlodinium citron, 

 Torodinium teredo, Poljjkrikos hofoidi, Noctiluca scintillans, Nematodinium 

 armatum (1917). Thus 24 species out of a total of 116 are common, while 92 

 are rare, being represented in a number of instances by records of a single 

 individual only. 



(2) Species are not equally abundant in different years. Thus Gymnodi- 

 niiim iiavnm was very abundant in 1914, but in no other year. G. coeruleum 

 was common in 1906, but not in 1917. PoJykrikos appears to be rather common 

 in most years. 



(3) There is some evidence as to favored haljitats. There is a distinct 

 arenaciphilous fauna, which we have previously noted, adapted to that region. 

 There are some species w^hich survive in larger numbers than others in the 

 immediately neritic waters, as shown in collections at the pier at La Jolla, but 

 this is doubtless in pai't due to relative numbers, and may be, in part, the result 

 of some vertical stratification. 



(4) The region of greatest variety in species begins several miles offshore 

 and is not in the innermost two to three miles. Many species found here 

 occurred also at the pier, but less frequently and in much smaller num])ers. 



(5) The number of species taken in surface hauls from the up])cr two meters 

 is nmch less than that taken in hauls from 80 meters to the surface. Hauls 

 from greater depths do not materially increase the number of species found. 



