PLANKTON OF THE WOODS HOLE REGION 1135) 
particular season (figs. 17 and 18). The following common tychopelagic forms 
appeared in the surface collections of the past year: Actinoptychus undulatus, Bid- 
dulphia alterans, B. favus, B. granulata, B. biddulphiana, B. rhombus, B. vesiculosa, 
Hyalodiscus stellager, Melosira borreri, and Paralia sulcata. All of these species are 
temperate forms. 
The oceanic and neritic diatoms that have a distinct periodicity in occurrence 
may be grouped according to the latitudes in which they are distributed. This 
method, originated by Cleve, has been used by almost all planktonologists. 
The various groups into which Cleve divided the characteristic plankton diatoms 
are represented at Woods Hole by the following species: 
Boreal Arctic___.-._..-___- Cheetoceros mitra. 
Nitzschia closterium. 
Thalassiosira hyalina. 
nordenski6ldii. 
North Temperate_________- Chetoceros danicum. 
debile. 
diadema. 
sociale. 
teres. 
Leptocylindrus danicus. 
Liemophora flavellata. 
Nitzschia longissima. 
Rhizosolenia feeroeensis. 
setigera. . 
Skeletonema costatum. 
Stephanopyxis appendiculatus. 
Synedra, gallionii. 
Thalassiosira, decipiens. 
Thalassiothrix nitzschioides. 
South Temperate__________ Asterionella japonica. 
Bacteriastrum varians. 
Cheetoceros cinctum. 
contortum. 
didymum. 
laciniosum. 
lorenzianum. 
schiittii. 
Ditylium brightwelli. 
Fragilaria crotonensis. 
Grammatophora marina. 
serpentina. 
Guinardia flaccida. 
Nitzschia paradoxa. 
Rhabdonema adriaticum. 
Rhizosolenia calear avis. 
delicatula. 
shrubsolei. 
Striatella unipunctata. 
Synedra undulata. 
cbropical¥s:< 425), “Savina e Bellerochea malleus. 
Rhizosolenia ealear avis. 
shrubsolei. 
Neritic_-------- 
