Vol. 54.] DIVISIONS OP SO-CALLED ' JTTEASSIC * TIME. 457 



Scaphitoid — ' Scaphites hifurcatus ' from the Upper Lias ; and that 

 is presumably a refracted Dactylioceras. 



These Scaphitoid forms are important, because, from phenomena 

 exhibited by them and by injured ammonites, it seems possible to 

 state as a biological law that there is a tendency to hypostrophy 

 — to revert to ancestral conditions upon any disturbance of 

 individual economy. Such disturbance may be : (1) suddeu, such as 

 an injury, and therefore local in action, restricted to the part 

 affected ; (2) long continued, such as unfavourable environment, and 

 therefore general, affecting the whole shell. The law is the same 

 in each case, and the results are similar : in the first case, a local 

 hypostrophy in the parts affected ; in the second case, general 

 hypostrophy. The acquirement in the second case is transmitted 

 to posterity ; but in the first the evidence of transmission is less 

 certain : attention may be drawn, however, to the case of Asteroceras 

 Slatteri (Wright). 



The shape of (EcoptycJiius refractus and CEc. Grossouvrei may be 

 regarded as the result of the efforts of a coiled cone to revert to the 

 ancestral form of a straight cone ; and the struggle between the 

 tendency to coil and the tendency to straighten produces the 

 peculiar shape. As there is no sign of local injury which would 

 reveal itself in displacement of the costae, the only conclusion would 

 seem to be that the forms are due to unfavourable environments. 



The Scaphitoid shape is, however, only an exaggerated exhibition 

 of the same process as that which produced the so-called abnormal 

 body-whorls — the tendency to excentric coiling. The different 

 degrees may be noted in Gervillii, huUatus, and refractus. 



In another family may be compared a series ending in Cadomo- 

 ceras, which, after all, denotes Scaphitoids (see p. 460). 



Note. — Of course the important point to establish is whether 

 Grossouvrei be a degenerative of Splicer oceras, and refractus a hetero- 

 chronous homoeomorphous degenerative of another series. If Gros- 

 souvrei be not the ancestor of refractus^ it cannot bear the name 

 (EcoptycTiius. Whether it have another generic name than Sphcero- 

 ceras is the merest matter of detail, but if it be only a form of 

 expression of a decadent Splicer oceras, it is doubtful whether another 

 generic name is required. The less decadent forms of Sphceroceras 

 are distinguished as Morplioceras. 



Family Hildoceratidse. 



I make the following notes concerning certain genera in this 

 family, but it may be remarked that all its genera will require very 

 considerable revision. This is now in preparation, in connexion 

 with my monograph on the ' Inf. Oolite Ammonites ' (Palaeont. Soc). 



It has been found that the curvature of the ribs in the species of 

 this family affords a generic criterion of the first importance. This 

 subject has not hitherto received sufficient attention, but in the 

 figures now being prepared in connexion with the monograph, it is 

 intended to give an outline of the rib-curve in all cases. 



