8o SECTIONAL ADDRESSES 



remain in which all coils are affected. It may, of course, be said that 

 more careful collecting from the lowest strata may show that these grades 

 do actually follow one another in time ; but taking the evidence at its 

 present face value it points to the simultaneous appearance of all grades 

 of the series, and suggests that the process at work is neither tachygenesis 

 nor proterogenesis but simultaneous mutation in the biological sense of 

 the term, and that the close resemblance to progressive evolution with 

 the passage of time is not due to evolution but to elimination. 



The conclusion thus suggested is so startling that the question naturally 

 arises as to whether any parallel to it is furnished by other groups of 

 fossils. For an answer it is unnecessary to seek further than Schindewolf 's 

 own examples. Among these is one, which has already been mentioned, 

 from among the foraminifera in the family Miliolides, which bear a 

 striking resemblance in form to the cephalopod family Lituitidce. Haeusler, 

 who is Schindewolf's authority for this example, tells us that the material 

 he describes came from the Lias of Banbury and was supplied to him by 

 Mr. Walford. The writings of the latter (1879) show that he collected 

 the material from a layer of blue clay only three feet thick at the base of 

 the Upper Lias. 



In this connection it is interesting to note that Rhumbler in dealing 

 with Bigenerina and Textularia, which are also quoted by Schindewolf in 

 support of the principle of proterogenesis, says that the change from 

 biserial to uniserial is so quick that the two forms occur side by side in 

 the same geological layer. In view of this it is just as reasonable to 

 regard this as a case of simultaneous mutation as of proterogenesis. 



In dealing with the Ostrea irregulare-Gryphcea incurva series attention 

 has already been drawn to the coenogenetic mode of appearance of the 

 habit of attachment. It may be noted here that the area of attachment 

 already exhibits a very wide range of extent in this very early liassic 

 species. Within the genus Ostrea this wide range remains quite constant 

 even to-day, but in Gryphcea this is not the case. Hitherto it has usually 

 been thought that in the evolution of the more fully coiled species the 

 area undergoes a progressive reduction in extent. This is not, however, 

 quite the correct way of stating the facts, for every grade of size already 

 existed in the O. irregulare stock. What really takes place is not a pro- 

 gressive reduction of area but a progressive elimination of larger areas, 

 leading to an increasing preponderance of small areas. This process of 

 elimination was certainly a vastly slower process than the original pro- 

 duction of the wide range of variation in size. So far as our knowledge 

 goes at present it seems as though this wide range was the result of some- 

 thing akin to an explosion of mutations. 



Among ammonites reference may be made to the subcraspedites fauna 

 of the basement beds of the Spilsby Sandstone. Here side by side in the 

 same layer, which is only several inches thick, occur a series of forms 

 ranging from S. prtmitivus, in which the whole shell possesses a fine 

 ornamentation, to S. cristatus, in which very coarse ribbing is dominant. 



It will no doubt be said that the deposits containing these very varied 

 forms are highly condensed, and that future work will prove that the 

 several varieties follow one another in a definite order of time. Meanwhile 



