PCECILOMORPHUS CYCLOIDES. 119 



/3. (Plate XXII, figs. 3, 4.) Similar, but with coarser ribs. 



y. Similar to a, but thinner (No. 8 on the foregoing Table). 



S. (Plate XXII, figs. 5, 6.) Very small umbilicus; much compressed form. 



8. (Plate XXII, figs. 9, 10.) Similar to a, but smaller umbilicus ; ribs more 

 numerous. 



Z. (Plate XXII, figs. 11, 12.) Similar to a, but smaller umbilicus, and only 

 strias on body-chamber. 



v. (Plate XXII, figs. 13 — 16, 19, 20.) Small umbilicus ; very thick whorls. 

 Should probably be considered the type-form. 



0. (Plate XXII, figs. 17, 18.) Slightly thinner than v, ribs irregular in size. 



i. (Plate XXII, figs. 21, 22.) Thin form, very evolute. 



Besides these, d'Orbigny has figured a form with large ribs at intervals (' Ceph. 

 Jurass.,' plate cxxi, fig. 3), which I do not possess. 



Of the above different forms, those marked a and y are by far the commonest ; 

 the forms (5, rj, 9 are rather scarce, while i is still scarcer, and the others occur only 

 occasionally. 



There is no species in the Inferior Oolite for which this ought to be mistaken, 

 if the sigmoidal character of the ribs be observed ; but I have noticed that 

 specimens of Sonninia Boiveri (J. Buckman) are very frequently placed in 

 collections under the name " Am. cycloides^ (Their ribs are straighter on the 

 lateral area, and they possess, when perfect, large, well-developed lateral lappets 

 to the mouth-border. Generally they exhibit small spines in the umbilicus ; but 

 these are sometimes absent, and it is then when the error is likely to occur. I 

 shall have to allude to these specimens later on ; and I hope then to place their 

 differences from the present species in a clear light.) 



Dr. Wright (' Monog. Lias Amm.,' p. 429) says : " The Ammonite which most 

 resembles Phyll. subcarinatum is the Phyll. cycloides, d'Orbigny, from the Inferior 

 Oolite of Moutiers ;" but to consider the latter a Phylloceras must be a mistake, 

 for it has nothing in common with that genus, neither ribbing, lobes, nor general 

 shape approaching those of the typical Phylloceras heterophyllum. It certainly 

 has some resemblance in shape to Am. subcarinatus, a species which should not, 

 however, be placed in Phylloceras? since its lobes have not the slightest Phylloceras- 

 character, though its form of ribbing is somewhat similar, being circular to the 

 whorl ; but this character at once separates it from Poecilomorphus cycloides. 



This species occurs rather frequently in the true Humphries ianum-zonej* the 



1 Dr. Haug (' Annuaire geol. universel,' tome iii, 1887, p. 134) states that Am. subcarinatus 

 belongs to Hyatt's genus Pelecoceras ; but Hyatt defined his genus as having an acute abdomen, and 

 his description seems to me to fit Am. serrodens, Quenstedt, a very different species. 



2 The lower part. I do not remember to have found it in the upper part, to which Mr. Hudleston 

 gives the name Cadomensis-beds. 



