GRAPTOLITES OF NEW YORK, PART 2 405 



in members of other genera (Diplogr. foliaceiis, Glossogr. 



q u a d r i m u c r o n a t u s) \'arieties and mutations possess homologous lateral 

 spines, while the)' are absent in the typical forms. 



It is probable that if true phylogenetic relations are to be made the 

 basis of subdivision, more than two groups of species are to be recognized 

 and that whole aggregations of characters and especially the form of the 

 thecae have to be used as criteria of distinction. Elles and Wood have in 

 the last instalment of the Monograph of BritisJi Graptolites which has 

 recently appeared, divided the genus Climacograptus by the characters of 

 the thecae, notably the direction of the free edge of the ventral wall and 

 of the apertural margin, and thus obtained five groups. These, in the 

 whole, coincide with the grouping here arrived at. 



One natural group within the species of Climacograptus here described 

 is formed by C . pungens, C . t y p i c a 1 i s and C . p u t i 1 1 u s . These 

 have in common the form of the neastic thecae, which are very long and 

 narrow, little overlapping and possess horizontal or slightly everted aper- 

 tural margins. In C . pungens and C. putillus this thecal form 

 persists throughout; in C. typicalis it is only characteristic of the 

 earlier rhabdosome. A further common character, which is very suggestive 

 of a close genetic relationship, is the presence of mesial mucros or spines 

 situated at the point of the second geniculation of the thecae, just above 

 the apertural excavations [see fig. 375]. C. pungens is the earliest of 

 these species ; it belongs to the third Deepkill zone and is probably of 

 Chazy age. C . putillus appears in a mutation in the Trenton and typi- 

 cally in the Utica shale; it is so closely related to C . pungens [see 

 Mem. 7, pi. 16, fig. 19, 20] that its direct derivation from that form can 

 not be doubted. C. typicalis is in the sicular portion of its rhabdo- 

 some hardly distinguishable from C. putillus, thereby indicating its 

 origin ; but then changes rather abruptly in the character of the thecae and 

 in size attained passes way beyond its relatives. C. innotatus Nichol- 

 son [1869, p. 238] from the Birkhill shales is apparently a younger British 

 representative of the same race, it possesses the same spines as C. typi- 



