RESUME. 139 



Am. Curioni may possibly be the ancestor of Lioceras and Pseadolioceras. 

 Both these genera have their ribs less curved — and therefore less developed — than 

 Harpoceras ; Lioceras does not possess such complicated lateral lobes as that genus, 

 but shows more auxiliaries, which probably owe their origin to the fact that, while 

 Harpoceras was in a transition state as regards the size of its umbilicus, this genus 

 had become fixed to the involute form. Lioceras shows ribs which are not 

 strikingly peculiar, except in one instance, namely, the V-shape. "Whether that 

 shape is due to atavism, or whether it is the result of a developed accidental pecu- 

 liarity, I cannot say. 1 The recession of the inner margin, and consequently of the 

 whorl, when the body-chamber is present, is a characteristic probably due to descent 

 from more evolute forms ; and so is the fact that the very young specimens — not 

 only in this genus, however, though it shows it the most, but in many other 

 genera — are extremely evolute, especially compared to the adults, and that great 

 inclusion does not commence in early youth. In several places I have noticed 

 these facts in the course of my remarks upon the genus. 



Pseudolioceras is another well-developed genus. It is highly involute, and has 

 evidently obtained that as a settled character. Dr. Haug says 2 that Pseudolioc. 

 compactile has more auxiliary lobes than Pseudolioc. lythense (none of my 

 specimens of the latter species show the lobes) ; but this fact might indicate that 

 the development of the auxiliaries to fill the lately-acquired increased breadth of 

 the side was actually in progress. This development of auxiliaries attains its 

 maximum in the next genus, Hyperlioceras, the descendant of this one. Here, 

 with one slight exception, we meet with highly involute forms ; but they have gone 

 a step further in the matter of development — producing more auxiliary lobes 

 to support the increased side-breadth — and they have enlarged the inferior lateral 

 saddle for the same purpose. Such species are Hyperlioc. discites and discoideum, 

 and probably Desori. But Hyperlioc. subdiscoideum is an instance either of 

 reversion or of less development in this matter of sutures (see p. 101); while 

 Hyperlioc. Walkeri has the full number of auxiliary lobes, but is an instance of 

 reversion in the matter of a wider umbilicus. That Hyperlioc. Walkeri is 

 descended from an involute Hyperlioceras is certain, because otherwise it would 

 not have inherited the extra number of auxiliary lobes. This parent Ilyperlioceras- 

 species (which we do not know at present) must have developed more auxiliary 

 lobes than its ancestor Pseudolioceras, and must have thereby given to the 

 increased side the necessary support. These lobes it has transmitted to its 

 descendants, Hyperlioc. discites, discoideum, and Walkeri. The last has, how- 

 appearance to the primary ribs in Ludwigia, but yet would, I think, be distinguishable. This would 

 not explain the small spines. 



1 Probably the former. Compare the recurved ribbing of the young of Ludwigia Murcliisonee, a 

 species standing lower in the scale of development. 



2 Op. cit., p. 623. 



