452 MISS E. M. E. WOOD ON THE LOWEE LT7DLOW [May I9OO, 



The genus Monograptus is represented in the Lower Ludlow by 

 fifteen well-marked species and thirteen varieties, while of the genus 

 Retiolites there are only two species. The following is a list of the 

 species and varieties described in this paper : — 



Genus Monograptus. Group I. Type M. dubius (Suess). 



M. dubius (Suess), M. vulgaris, sp. nor., M. vulgaris var. a, M. vulgaris 

 var. (5, M. tumescens, sp. nov., M. tumescens var. minor (M'Coy), 

 M. gotlandicus, Perner, M. co?nis, sp. nov., and M. ultimus, Perner. 



Group II. Type M. colomis (Barr.). 

 M. colonus (Barr.), M. colo?ms var. ludensis (Murch.), M. colonus var. 

 compactus nov., M. varians, sp. nov., M. varians var. a, M. varians 

 var. /3, M. varians var. pumilus nov., and M. Rmneri (Barr.). 



Group III. Type M. chimcera (Barr.). 

 M. chimeer a (Barr.), M. chimarav&r. Salweyi (Hopk.), M. chimmravnx. a, 

 M. leintwardinensis, Hopk., and M. leintwardinensis var. incipiens nov. 



Group IV. Type M. uncinatus, Tullb. 

 M. uncinatus var. orbatus nov., and M. uncinatus var micropoma (Jaekel). 



Group V. Typeilf. scanicus, Tullb. [sub-group of M. lobiferus(M. l Coy)]. 

 M. scanicus, Tullb., and M. crinitus, sp. nov. 



Group VI. Type M. Nilssoni (Barr.). 

 M. Nilssoni (Barr.) and M. bokemicus (Barr.). 



Genus Ketiolites. B. nassa, Holm, and B. spinosus, sp. nov. 



Of the six groups of Monograptus enumerated in the foregoing list, 

 the first two, those of M. dubius and M. colonus, are by far the most 

 important, and both are rich in species and varieties. The sepa- 

 ration of these two groups has been almost entirely determined by 

 the character of the proximal extremity, for the general form of 

 the polypary and the shape of the thecse are much the same in 

 both groups. Although the group typified by M. colonus is the 

 more characteristic of the Lower Ludlow Shales, being entirely 

 confined to them, ) r et I place the group of M. dubius first, as it is the 

 more primitive of the two and is well represented in the under- 

 lying AVenlock Shales. 



The separation of the group of M. chimcera as distinct from that 

 of M. colonus must be regarded as provisional: for the presence or 

 absence of thecal spines, as I have already pointed out, seems to be 

 in many forms dependent on external conditions, and therefore 

 can hardly be considered of great classificatory value. 



The remaining three groups, those of M. uncinatus, M. scanicus, 

 and M. Nilssoni, are individualized almost entirely by the character 

 of the thecae and the form of the polypary. Such grouping is 

 admittedly unsatisfactory and provisional, but these groups are so 

 poorly represented in the Lower Ludlow Beds that there is not 

 sufficient evidence available for a more complete and exact classifi- 

 cation. I am of opinion, however, that further research will show 

 the advantage of placing species with such distinct proximal ex- 

 tremities as M. Nilssoni and M. bohemicus in separate groups ; and 

 possibly of uniting M. scanicus and M. Nilssoni in the same group 

 on account of the similarity of their siculse. 



When we compare the graptolite-fauna of the Lower Ludlow as 

 now worked out, with that of the Wenlock Shales below, the sup- 





