202 Evolution and Distribution of Fishes 



But the apparent mixing of records for two adjacent 

 sets of beds, and the accurate placing of them for another 

 in adjoining sentences, is evidently set forth in de Lappar- 

 ent's work (<57 : 1 141-42). For on page 1141 he gives 

 from Mazenay in "calcaires fissiles" of the Jurassic,L^/)^o- 

 lepis constrictus and L. affinis — both of which we regard 

 as freshwater — along with Lioceras serpentinum and Ino- 

 ceramus c'mctiis, both typically marine. But at top of the 

 adjoining page he gives from Souabe in "schistes-bitumi- 

 neuse ou schistes-carton" five strata in descending order 

 thus : 



(5) schistes a Belemnites tripartitus et Inocerames. 



(4) schiste et calcaire a Lioceras serpentinum et Belemnites 



gracilis. 

 (3) Calcaire a poissons {Ptychodus, Leptolepis, Lepidotus) . 

 (2) feuillet a Posidonia Bronni. 

 (i) couche de passage a Monotis substriata. 



The two upper and the lowest at least are typically marine 

 beds. (3) and (2) however are freshwater. Ptychodus 

 moreover is a Cretaceous not Jurassic genus. One of those 

 oscillations between land and sea evidently occurred here, 

 such as were frequent through the entire Jurassic. 



A very similar state of affairs is that set down by 

 Brodie (pp. 57-58), where he described a "bone-bed" with 

 associated PuUastra arenicola, but when in an exact tabu- 

 lated list he states that this bone-bed is "a hard thin stratum 

 full of pyrites, and composed of bones, scales, and teeth 

 of fish," and that "connected with this is a white and yellow 

 sandstone full of casts of PuUastra arenicola'* we recognize 

 that the two were totally distinct. The latter was a marine 

 bed, then above it and doubtless after sudden elevation 

 of the region and probably by volcanic dust-deposit, a mass 

 of freshwater fish-remains became entombed, these fishes 

 agreeing with species that de Lapparent often refers to 

 amid typical freshwater setting. 



A suggestive paper by Roberts "On the Correlation 

 of the Upper Jurassic rocks of the Swiss Jura with those 

 of England" contains extensive lists for Mid and Upper 

 Jura. These include varied and abundant marine inverte- 

 brates, but not a single plant remain, Estheria or fish. But 

 passing to the Purbeck strata on top of the series he gives 



