1920 CHRONOLOGY 



morphs, nomomorphs and phaulomorphs : the first might have had no 

 cause for retreat ; the second might have had to retreat occasionally, 

 and the last might have been in a fairly constant condition of darting 

 away. Production of phaulomorphs instead of megalomorphs might 

 have been brought about by over-population, by decrease of food supply, 

 by increase of competitors, other than cephalopods, for the available 

 food. Ammonoid phaulomorphs abound during Inferior-Oolite times, 

 when the ammonite population reached its acme in numbers of species, 

 of specimens, and almost of diversity ; for there are aberrant forms 

 evolved — criocones, toxocones and baculicones, possible attempts to 

 find a solution of the problem of avoiding enemies, trying to attain again 

 to the orthoconic condition, which, at any rate, so far as small forms 

 were concerned, must have been fairly suitable for the purposes of rapid 

 retreat. This tendency towards the orthoconic seems to have been 

 hampered by ancestral traits of coiling cones trying to assert themselves ; 

 and thus when a fairly orthoconic development had been attained, 

 ancestral characters revive in old age, and make for curvature again — 

 the curious walking-stick crook at the end of a straight piece. 



It is in the Cretaceous that the aberrant forms show the greatest 

 development. This cannot have been because of over-population so far 

 as Ammonite competitors are concerned, but it might, perhaps, have 

 relation to the greater development of some other marine organisms. 



The peculiar suitability of the shape of a goniocone for darting away 

 has been already mentioned ; but now comes an interesting question : 

 in addition to side-lappets or auricles to the conch-aperture, this form 

 has developed a sort of cowl-shaped rostrum on the median line of the 

 periphery. Rostra of less developed patterns are a feature of oxycones ; 

 but many well-auriculate forms — cadicones, spharocones, and their 

 serpenticonic developments — lack the feature : with them the portion 

 of the periphery connecting the auricles is neither sinuate nor rostrate, 

 but annulate, that is, quite straight. With such periphery, or with 

 simple rostra, there would be no interference with the action of the funnel ; 

 but the case is altered with an incurving rostrum. Is it surmisable that 

 in such rostrate forms the funnel had been developed in duplicate, like 

 the twin screw of a liner, acting not only for quicker propulsion, but 

 making for more rapid turning ? 



It may be noted in regard to those forms which have developed 

 lateral lappets with annulate connecting band that, in a sense, they 

 have reproduced something similar to the hyponomic sinus of the 

 Nautiloids ; for the plan of the lappets and band make a U or sinuate 

 curve. See Trilobiticeras and Otoites, Pis. CXL, CXLI. 



Further remarks on the subject of Development must be held over 

 until more progress has been made with the illustration of species and the 

 naming of genera. Incidentally it may be remarked that the detailed 

 naming of genera gives great advantage in the discussion of develop- 

 ment, faunal distribution, chronological sequence, and other phenomena. 

 By one word it is possible to lay the finger on the particular restricted 

 lineage required, and thus to express its characters — cumbersome peri- 

 phrasis is avoided, and greater precision of expression is attained with 

 needful brevity. 



Chronology 



See T.A. Ill, 5, Editorial ; for Chronology of Lower Oolites see 

 Y.T.A. II, x, and ' Brach. Namyau ' ; Pal. Ind. N.S. Ill (2), 1917, 

 236-239 ; for Middle Oolites see ' Kell. R.' ; Q.J.G.S. LXIX, 1913, 

 p. 160. These tables are not yet satisfactory : all will require emendation 

 and possible expansion — exact chronological work is only just beginning. 



