HAUGIA ESERI. 157 



line distinctl}' tells us, to the genus Hammatoceras ;^ and it is, like Hamm. amalthei- 

 forme, Hamm. climacomphalum, &c., one of the species of that genus which has 

 lost the characteristic inner-marginal knobs. 



That this species is descended from H. occidentalis appears most probable ; and 

 yet the fact that often — but not always — the ribs disappear in the latter at an 

 earlier age and are also less conspicuous, is not correct from this point of view. 

 If H. Eseri then is descended from one species of tubercled Haugia — say H. jugosa 

 — and H. occidentalis from another — say H. variabilis — we should be justified in 

 keeping the two forms separate. 



That both H. Eseri and H. occidentalis represent the further development of 

 the senile stage of a species of tubercled Haugia is very plain from their suture- 

 line ; but more than this the fascicled ribs of the instructive specimen figured in 

 Plate XXV, fig. 7, are an exact reproduction of the ribbing of H. variabilis 

 with an appearance of very rudimentary knobs. 



Fascicled ribbing is to be observed not only in this specimen but more or less 

 in many others. On the inner whorls of the umbilicus of the specimen depicted in 

 Plate XXVI, fig. 1, the ribs are distinctly gathered into bunches. (This has not 

 been sufficiently brought out in the figure.) 



Practically speaking, what may be called the tubercled stage has ceased to be 

 reproduced in consequence of the earlier assumption of senile characters. It is 

 very important that the reason for the loss of tubercles should be correctly under- 

 stood ; because otherwise it might be supposed — as it has been already — that 

 Haugia occidentalis and H. Eseri were allied to Grammoceras, or to the group 

 which I have placed in the genus Pseudolioceras. There is no doubt that in 

 shape they both converge towards various members of those genera. For the 

 differences between Haugia Eseri and Pseudolioceras and between it and Grammo- 

 ceras see generic description, pp. 143, 144. 



An interesting fact in connection with this characteristic Cotteswold Ammonite 

 is that a species very nearly allied to, if not practically identical with it, is men- 

 tioned by Gottsche^ as occurring in the Cordilleras of the Argentine Republic. 

 Of his Harpoceras Andium Gottsche says : — " H. Andium . . . steht . 

 keiner Art naher als dem H. Eseri, Oppel . . . ., indessen ist unsere Art 

 durch den Querschnitt, die weniger geschwungenen Rippen, und das Fehlen 

 einer wirklicher Nabelkante geniigend unterschieden." Fig, 8 in his pi. i 

 appears most like H. Eseri ; but the specimen depicted in pi. ii, fig. 2, has 

 a peculiar aspect of ribbing which excites my suspicion, and causes me to think it 



^ Haug, " TJeber Folymorphidce," 'Neuee Jahrbuch fiir Mineral., &c.,' Bd. ii, p. 91, footnote, 

 1887. 



2 " TJeber jurassiche Versteinerungen aus der argentinischer Cordillere," ' Palaeoutographica,' 

 Suppl. iii. Lief, ii, Heft 2, Cassel, 1878. 



