440 Annals New York Academy of Sciences 



hypotheca; hanging-drop configurations to subspherical forms with a tapered 

 hypotheca and bearing or lacking antapical horns (Peridinium), an eccentric 

 expression of the same configuration with partly deflected apex and horns 

 (Heterodinium); bizarre, multihorned Ceratium in which horns may deflect at 

 all angles and in all directions.^^ -^ 



Nine varieties of Ceratium hirundella were found in various European 

 waters.- '^^ Size variants have been reported from different Swiss lakes: 92 ju 

 in Lake Como, to 707 n in Lake Schwendi.-'' SampHng several ponds in the 

 vicinity of Darmstadt, Germany at 2-week intervals over a 5-year period, 

 Ljg|-29a found that population density fluctuated with rise and fall of tempera- 

 ture. He noted seasonal variation in both horn length and horn number in 

 C. hirundella. In the summer four-horned type, for example, horns were 

 shorter during very hot summers than they were during cooler ones. Ap- 

 parently, in fresh, as well as marine waters, horn development is an adaptive 

 modification to resist sinking below optimal food and sunUt levels. 



Flaring, sail-like, structures from the girdle, inverted umbrella and parachute 

 type membranes as in Ornithoceras, Diuophysis, and other forms'* ■-'' all tend to 

 increase the surface area of the anterior over the posterior. In turn, this helps 

 to orient properly the given protist. 



A third group of protists of polyphyletic origin are the hystrichosphaerids. 

 Many forms classified under this group are apparently dinoflagellate cysts.i -^^ 

 Fossils often show dinoflagellate plates although many forms lack a distinguish- 

 able plate system. Configuration of the central body is often globular but all 

 variations are known from subround and ovate to subelUptical. Arising from 

 the central body are spines or tubular processes, or both, with flattened or 

 bifurcate terminations. It has become clear that these tubular processes were 

 originally connected to a circumscribing membrane. A recently found globular 

 hystrichosphaerid from the Kansas Cretaceous bears a short, tubular process 

 that terminates in two fine flagella-Hke extensions within the body of the en- 

 closing membrane. ^^ 



For those hystrichosphaerids which are definitely dinoflagellate cysts, 

 morphology was determined by encystment. HystrichospJiaera furcata and 

 H. speciosa bear an equatorial girdle and dinoflagellate plates, and are good 

 examples. Generally, hystrichosphaerid form is a variation of the spherical 

 configuration. Why this is so can best be understood if one observes a cyst 

 inside a subtriangular-to-buUet-shaped dinoflagellate like Deflandrea phos- 

 phoritica?- The spherical shape is the most efficient configuration that can be 

 enclosed in the volume available. 



Radiolarian Scleratoma and Tiniinnid Lorica 



Radiolarians and tintinnids occur together in the Mesozoic fossil record in 

 the Mediterranean area^^ and hence it seems desirable to discuss them together. 

 Both groups have living representatives which occur in great abundance. 

 Radiolarians found in the fossil record are almost invariably "upper-zone 

 pelagic types"^^ although abyssal forms are known. 



Although radiolarians are incapable of horizontal locomotion, tintinnids can 

 swim rapidly by the aid of bristles and cilia.^* Both forms had to solve the 

 problem of resisting passive sinking below optimal levels of the sea. 



