PLANKTON OF THE WOODS HOLE EEGION 
115 
particular season (figs. 17 and 18). The following common tychopelagic forms 
appeared in the surface collections of the past year: Actinoptychus undulatvs, Bid- 
dulpTiia alterans, B.favus, B. gramtlata, B. hiddulphiana, B. rhombus, B. vesiculosa, 
Hyalodiscus stelliger, Melosira horreri, 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 : 
Neritic. 
Boreal Arctic. 
North Temperate. 
South Temperate. 
Tropical- 
Chsetoceros mitra. 
Nitzschia elosterium. 
Thalassiosira hyalina. 
nordenskioldii. 
Chifitoceros danicum. 
debile. 
diadema. 
sociale. 
teres. 
Leptocylindrus danicus. 
Licmophora flavellata. 
Nitzschia longissima. 
Rhizosolenia fseroeensis. 
setigera. 
Skeletonema costatum. 
Stephanopyxis appendiculatus. 
Synedra galHonii. 
Thalassiosira decipiens. 
Thalassiothrix nitzschioides. 
Asterionella japonica. 
Bacteriastrum varians. 
Chietoceros cinctum. 
contortum. 
didymum. 
laciniosum. 
lorenzianum. 
schiittii. 
Ditylium brightwelli. 
Fragilaria crotonensis. 
Grammatophora marina. 
serpentina. 
Guinardia flaccida. 
Nitzschia paradoxa. 
Rhabdonema adriaticum. 
Rhizosolenia calcar avis. 
delicatula. 
shrubsolei. 
Striatella unipunctata. 
Synedra undulata. 
Bellerochea malleus. 
Rhizosolenia calcar avis. 
shrubsolei. 
