part 2] GEOLOGICAL HISTORY OF THE GENUS STRATIOTES. 129 1 



Affinities. — See Stratiotes thalictroides (below). 



It is interesting to notice that Bristow (21) realized that two. 

 species of Stratiotes occurred in the Hamstead Beds. In his list 

 of fossils he refers to these as Folliculites parisiensis Brongniart 

 and F. thalictroides Brongniart respectively. This point ha& 

 always been overlooked by other workers, who not only failed to 

 discriminate between the two Hamstead species, but also between 

 the Hamstead, Bembridge, and Headon species in the Isle of 

 Wight. 



5. Stratiotes thalictroides Brongniart. (PL V, figs. 13-14 

 & PL VI, figs. 6-8.) 



1822. Carpolithes thalictroides var. A. -parisiensis (Ad. Brongniart 2). 



1822. C. thalictroides var. A. parisiensis (Ad. Brongniart 3). 



1833. Folliculites thalictroides var. parisiensis Brongniart (Zenker 7). 



1849. C. thalictroides (Ad. Brongniart 9). 



1862. F. thalictroides Brongniart (Heer & Pengelly 22). 



1893. C thalictroides var. parisiensis Brongniart (Nehring 44). 



Seed oblong, narrow, almost cylindrical, but slightly flattened 

 laterally, sigmoidal ; keel narrow, convex exteriorly, with a small 

 beak at the apex, broadening gradually towards the apex, not con- 

 tinued round the base, merging gradually into the collar ; collar- 

 moderately large, rounded ; testa ornamented from neck to apex 

 with longitudinal ridges which terminate in the beak, ridges absent 

 or feebly developed on the keel ; pitting coarse, except along the- 

 dorsal margin of the keel where it is very fine ; micropyle sub- 

 basal, slightly oblique ; digitate cells obscure. 



This species differs in its mode of preservation from all others, 

 examined. It occurs as casts, both internal and external, in a 

 siliceous limestone ; such casts as were available for study showed 

 the complete external form and sculpture, but (of the interior) 

 only the basal half. 



Despite this fact, a comparison of the characters of S. thalic- 

 troides and of other species lends a high degree of probability to- 

 the following inferences : — 



(1) The dorsal wall would appear to broaden towards the apex. 



(2) The hilum would seem to be associated with the apical beak on the 

 dorsal margin : it certainly cannot have occupied a position below the middle- 

 of the dorsal margin, as is seen by studying the available internal casts. 



(3) The raphe would seem to be short and transverse, for this form of 

 raphe is associated with the sigmoidal form of Stratiotes seed. 



Dimensions. — Length=7'5 to 8 mm.; breadth =2 to 2*5 mm.. 



Horizon. — Upper Oligocene, Calcaire de Beauce. 



Localities. — Longjurneau, Seine-et-Oise (in the Meuliere 

 superieure, Chattien-Formitien) ; Villiers, near Pontchartrain ; 

 Palaiseau ; Villeginis ; Cbapelle Milon, near Chevreuse. 



Affinities. — The distinctive features of the species are its 

 great length and relative narrowness (see p. 123) as also its sig- 

 moidal form. The nearest allied species is S. websteri, which 

 occurs at a lower horizon in the Oligocene (see p. 128). 



