HAUGIA AND GRAMMOCERAS. 



221 



Remarks on the Genera Haugia and Grammoceras, 



In the foregoing pages I have expressed my views upon the relationship of the 

 various members of these genera in the articles concerning the different species. 

 The theory that Haugia is descended from Lillia causes the former to be regarded 

 as the " cousin " of Ludivigia ; and it is interesting to observe the differences 

 which may be developed in two genera sprung from the same source. 



In Grammoceras we have a large and influential genus to deal with — a genus 

 which dominated the Jurense- and the Opalinimi-zone. It may be reckoned to 

 contain altogether thirty-one so-called species, ranging from the Jamesoni- to the 

 Murchiso7ige-zone inclusive. Out of this number, twenty forms, more or less 

 entitled to the name of species, have been dealt with in this Monograph ; and these 

 are disiributed into the Murchisouse-zone — 1, the Opalinum-zone — 9, and the 

 Jiirejise- zone — 10. It may be useful to give a table showing the probable 

 relationship of these species ; because such a table will demonstrate at a glance 

 what can only be gathered otherwise from the perusal of many pages. I have 

 stated that I cannot satisfactorily identify the ancestor of the species now dealt 

 with, and that, although several species of the genus appeared before the Jurense- 

 zone, yet I do not attribute the parentage to them (p. 163). 



Table IV. — The Grammocerata. 



Murchisonae- - - G. nannodes 



zone 



f G. leurum 



Opalinura- J G. subser- G. costu- G. sub G. aalense — G. lothaiiugicum 



zone I rodens latum comptum I 



Jurense- 

 zonc 



(^ G. mactra G. distans 



G. fluitans 



Q. striatu- 

 lum 



G. Orbignji G. doerntense G. dis- G. Muellcri-r-G. Bing G.falla G.Cottes- 



I I I pansum | maiiiii ciosum woldia. 



I I I G. .subquadiatuui 



-G. toarceuse G. toarcense, G. metal- | 



with joined larium G. quadratum 

 ribs 



Table IV shows that, with trifling exceptions, I have traced the Ch^ammocerafa 

 to two sources — the solid-carinate to Gramm,. toarcense, the hoUow-carinate to 

 Oramm. quadratum ; but whether the source of these two species is really very 

 widely separated is a point which I cannot determine at present. In a great 

 measure this is due to the apparent paucity and isolated character of the species of 

 Grammweeras in the zones below that of Jurense. In the Jurense- and Opallnum- 

 zones we have a very fairly compact series ; and it must truly be said that it is often 



