100 Univet'sity of California Publications. [Zoology 



In any ease this spine in Triposolenia lies near the suture and 

 the continuation beyond the spine is also near the sagittal line 

 and may well belong to the right valve. Not having- seen Tripo- 

 soloiia in the stage of division it cannot be stated positively that 

 the ventral fin would be parted at this spine and that the anterior 

 and posterior moieties would go to the left and right valves re- 

 spectively, but the homologies here indicated make such a division 

 probable in this genus. The right list continues but a short dis- 

 tance beyond the pore, and lies on the side of the cytopharyngeal 

 enlargement. In Peridinimn and Binopliysis the longitudinal 

 furrow lies posterior to the flagellar pore. Its homologue there- 

 fore in Triposolenia is the very short extension of the two lists 

 posterior to the pore. The long anterior section may be regarded 

 as a posterior extension of the lists of the transverse furrow 

 affording a channel for the passage of the transverse flagellum 

 {tr.fl. PI. 16, fig. 6) from the pore to the girdle, and it may there- 

 fore be regarded as a pseudo-longitudinal furrow resulting from 

 the migration apart of the transverse furrow and the flagellar 

 pore and the extension of the lists in this region of migration. 



The transverse flagellum (tr.fl. PI. 16, fig. 6) arises in the 

 flagellar pore and passes anteriorly between the longitudinal 

 lists and encircles the head from left around to right as in other 

 girdled Dinoflagellates. The longitudinal flagellum I have not 

 seen in any species thus far examined. The rudimentary longi- 

 tudinal furrow is suggestive of a possible reduction to a rudimen- 

 tary state. 



The flagellar pore (f.p. PI. 16, fig. 6) is a large opening on 

 the antero-ventral end of the cytopharyngeal expansion. Its left 

 lip is somcAvhat higher than the right and it is therefore directed 

 anteriorly and to the right. 



The protoplasmic contents are very hyaline and coarsely gran- 

 ular and contain a compressed ellipsoidal nucleus (nu. PI. 15, 

 fig. 2), with a moniliform chromatin reticulum. Near the nucleus 

 is found a pusule (pus. PL 15, fig. 2) which opens by a slender 

 canal {can. PL 15, fig. 2) into the flagellar pore. One or more 

 accessory pusules {ac.pus. PL 15, fig. 2) may lie near it in the 

 plasma. Occasionally the plasma is crowded with highly refrac- 

 tive ellipsoidal plasmosomes of amyloid character. In many 



