SONNINIA— SUMMARY. 441 



SUMMARY. 



The illustration of the Sonninise of the Concavum-zone has occupied rather 

 more than 47 plates, even though considerable reductions from natural size — 

 not always, it is to be feared, to the advantage of the student — have been made. 

 As many as 110 specimens 1 yielding 71 named species have been represented in 

 327 figures; yet this goes but a little way towards making anyone acquainted with 

 the various forms of Sonninia which are comprised in the fauna of the Concavum- 

 zone. Setting aside the fact that the tale of species is obviously incomplete, there 

 are very many cases in which the young and immature forms have not been illustrated. 

 Continental correspondents have particularly asked that the young and immature 

 forms of the species of Concavum-zone Sonninia? should be figured as well as the 

 adults ; but, partly on account of space, it has not been possible to comply with 

 their requests. If they knew the work that is still before me, even to illustrate 

 the Ammonite-fauna in the same confessedly imperfect manner, they would not be 

 surprised at this. 



There are three species of Concavum-zone Sonninice of which the septa of the 

 types remain unknown, namely, Sonn. decorata, Sonn. crassinuda, Sonn. densi- 

 costata. The first two have been placed with species to which they bear external 

 resemblance; the last, when critically considered, is found to have no close 

 external resemblance to any of the other species of the Concavum-zone, but it 

 seems to be more nearly allied to species of higher horizons — to be described 

 later on. 



The following Table shows the various skeleton outlines of the different 

 Sonninise which have been mentioned in the previous pages. For facility of 

 comparison they have been brought together on one page, and thus the differ- 

 ences between them may be readily noted. No attempt has been made to 

 arrange them according to their various degrees of development — that the reader 

 can easily see for himself ; and so they have been placed in the order in which 

 they have been referred to in the foregoing pages. The explanation on page 442 

 gives the source from which each one has been taken. 



1 Not counting those from which suture-lines only were taken. 



56 



