MORPHOLOGY AND TAXONOMY OF MASTIGOPHORA 277 



inter])reted them, are zones of growth occurring after the plates are 

 formed. Schiitt on the other hand regards them as special ribs or 

 thickenings for the purpose of strengthening the shell between the 

 plates. Kofoid dissents from these views and suggests that the 

 intercalary striae are modified pores or canals lying in the wall and 

 may be adaptations for further communication between the proto- 

 plasmic body and the environment. IVIany of the Peridinidas have 

 shells which are more or less uniformly perforated by fine canals and, 

 although the inner openings of these pores have not been definitely 

 made out, it is probable that they serve the same function. 



The region about the flagellum pore is covered by plates of more 

 delicate type than those of the rest of the shell and the plates are 

 more difficult to make out but there appear to be four such plates 

 in the species of Peridinium, one of which, the rhomboidal plate, 

 may be larger than the others, and this plate, in the genus Ceratium 

 becomes the main protection of the oral region. 



The flagellar pore is an opening through the thecal wall some- 

 times with thickened walls which form a tube running a short dis- 

 tance into the inner protoplasm. In many cases both fllagella 

 emerge from one such pore but in a large number of forms there 

 are two flagellar pores, one for each flagellum (Fig. 132). Schiitt 

 regards the single pore as more primitive. 



Family 2. Dinophysidae, Stein, Bergh.— Plates, characteristic of 

 the Peridinidffi are here absent. The shell also, is built on quite 

 a different plan of structure, agreeing with that of the Adinina in 

 consisting of two lateral valves united in a sagittal suture with 

 interlocking teeth, and passing vertically through the longitudinal 

 groove or sulcus. * The transverse groove-annulus is high up on 

 the body and is often provided with wide lamellae. The epitheca 

 and hypotheca, therefore, are widely different in size. In Amyhi- 

 solenia the former becomes almost rudimentary and suggests a 

 transitional form to the Adinina. Asymmetry is characteristic and 

 frequently leads to fantastic form relations. Phseosomes or peculiar 

 brownish masses, are regularly present and brown or yellow chroma- 

 tophores are often present although many representatives of the 

 family have none at all. They are confined mainly to the warmer 

 seas. 



Family 3. Phytodinidse, Klebs.— This family, created by Klebs 

 as a subdivision of the Diniferida, includes forms which more nearly 

 resemble plant cells than Protozoa. With the exception of the 

 yellow-brown chromatophores, radial protoplasmic structure and 

 cellulose walls, there are few Dinoflagellate characteristics. They 

 lack both longitudinal and transverse grooves and have no flagella. 

 Reproduction occurs by simple division, the daughter cells either 

 separate by rupture of the cellulose wall (Phytodinium) or form 

 GJoeocystis-\We colonies. In the latter case thick gelatinous mem- 



