28 TYPE AMMONITES— III Nov. 



defined, but distinguished by the lower stage of development of the 

 s.l., by stronger ribs on the periphery and perhaps by remaining 

 dichotomous and not passing to tritomous ribbing. Subsequently it 

 develops similar massive ribs in old age — D. ingens Young & Bird sp. 

 PI. CLXXXIV ; D. varioco statu m, Buckland sp. (Healey, Q.J.G.S. LX, 

 1904, 58 f . 2 ; xi ; Pal. U. 56). 



Grossouvria, Siemiradzki, Oct. 1898, Mon. Perisph. ; Palaeonto- 

 graphica, XLV, pp. 78, 79. " I. Abtheilung. Subgen. Grossouvria nob. 

 A. Mutationsreihe des Per. subtilis " (p. 79). 



This makes Per. subtilis the indicated genoholotype, which may be 

 fixed with further precision on the holotype of the species, Neumayr, 

 Balin, xiv, 3. 



Before proceeding further it is advisable to note the different 

 methods by which costate serpenticones (Perisphinctean forms) have 

 been produced in the Inferior Oolite ; for it is here that change over 

 is seen to advantage — the inner whorls, sometimes till quite late in life, 

 so different from the outer, which are Perisphinctean. 



A. Inner whorls. B. Outer whorl or whorls. 



Bullate cadicone, Costate serpenticone, 



Docidoceras. Docidoceras. 



Tuberculate serpenticone Costate serp. 



(Skirroceratan) . 

 Tuberculate serp. with Costate scrp., 



sulcate venter (Parkinsonian). Canmontisphinctes. 

 Tuberculate serp., Costate serp., 



zigzag ornament. Procerites. 



Sphaeroconic with constrictions Costate serp. No parabolic 



(Morphoceratan). curves, Am. defrancii. 



Differences of inner whorls, when there are several whorls before 

 a change takes place, are good evidence for difference of origin, but 

 differences of embryonic whorls only are not good necessarily — omission 

 due to lipopalingenesis and modifications due to brady- and pro- 

 palingenesis have to be allowed for. 



The Perisphinctidae, as now defined, showing parabolic curves, 

 considered to be intermittent zigzag ornament, have presumably come 

 from a later development of 4A, having taken a road different from 4B — 

 preserving relics of zigzag ornament and not losing all that ornament 

 suddenly- 



Of the above, 1 belongs to the Sphaeroceratida;, 2 to the Stepheo- 

 ceratidae, 5 to the Morphoceratidaa. Thus 3 and 4 are left. 



Family PARKINSONIDM, nov. 



Descendants of coronates which acquire more or less of peripheral 

 sulcation and at this stage have a comparatively simple s.l. They 

 pass on the one hand into uncoiled forms and on the other hand into 

 costate serpenticones : these develop constrictions, lose the peripheral 

 sulcation more or less completely and may elaborate the s.l. A stage 

 with parabolic curves is not developed. 



In the early Perisphinctean forms (costate serpenticones) the 

 coronate stage with lateral tubercles and the sulcate stage with some- 



