part 4] THE EVOLUTION OF THE LIPAKOCEEATID.E. 271 



Lipabocehas cheltiense (Murchison). (PL XXI, tigs. 4 rt-4 d ; 

 text-rigs. 4 a & 4 b, p. 270.) 



Eefigured, ' Palaeontologia Universalis ' pt. iii, ser. 1 (1905) No. 67. 

 Dimensions of figure : — 



Diameter. Whorl height. Whorl thickness. Umbilicus. 



93 mm. 45 per cent. 67 per cent. 24 per cent. 



In the type-specimen the early part of the last whorl is similar 

 in shape and ornament to L. obtusinodum. Towards the end of 

 the whorl, however, the whorl height increases and the periphery 

 becomes more strongly arched, while the unpaired rounded tubercles 

 give place to paired bullae or transversely extended tubercles : this 

 return to paired tubercles is the first indication of catagenesis. 



The details of the suture in the type-specimen are not discernible ; 

 but it is clear that the external saddle is narrower than the first 

 lateral lobe, the latter bein°* mainlv ventral to the outer tubercles. 

 (British Museum — Natural History, Xo. 74955 a.) 



Development of Liparoceras clielt ie use. — The specimen, 

 examined was collected at the Battledown Pit, Charlton Kings, 

 Cheltenham (PI. XXI, figs. 4«-4rf). The innermost whorls are not 

 preserved, but at a diameter of 10 mm. the shell is quite smooth, 

 the whorl being stouter and the form more involute than in the 

 adult. The whorl thickness is equal to nearly three-quarters of the 

 diameter until a much later stage ; it is interesting to note that 

 this condition is lost in L. sparsicosta at a diameter of 1 mm. 

 In L. cheltiense there is a gradual change from the young to the 

 adult form of whorl. 



Fine tubercles are seen at a diameter of 10 mm. ; they are 

 already unpaired and are united by very feeble ribs which cross the 

 venter (PI. XXI, figs. 4 c & 4*d). Faint longitudinal striation is 

 also present. 1 The young suture is more complicated than that of 

 L. sparsicosta ; for example, the suture of L. cheltiense at 8 mm. 

 diameter has the first lateral lobe nearly as deep as the external 

 lobe, a condition which is not attained by L. sparsicosta until 

 much later. 



Diameter. 



Whorl height. 



Whorl thickness. 



Umbilicus. 



70 mm. 



48 per cent. 



56 per cent. 



20 per cent. 



38 



50 



70 



19 



25 



50 



72 



— 



13 



54 



73 



15 



Young specimens of L. cheltiense (up to a diameter of 30 mm.) 

 bear a superficial resemblance to Secheiceras bechei. They may 

 be distinguished by their sutures (even at this diameter the first 

 lateral lobe of B. bechei is deeper than the external lobe) and by 

 the more depressed whorl of L. cheltiense ; further, while tubercles 



1 Compare A. striatus Quenstedt, ' Petrefactenkunde Deutschlands : Cepha- 

 lopoden ' vol. i (1849) p. 135 k pi. ix. tig. 24. 



