GKAPTOLITES OF NEW YORK. PAUT 1 (i57 



T . q u a d r i b r a c h i a t u s in a sandy slate between Def reestville and West 

 Sandlake, Rensselaer co. N. Y. [T. N. Dale, coll.J In the second instalment of 

 the Monograph of the British Graptolites, which has just appeared, the species 

 as defined by Hall has been split and a part separated as T. amii. This new 

 species is common in graptolite bed 2, and its separation will make T . s e rr a 

 a less frequent form in that bed. Also the form, listed as a smaller mutation 

 of T . s e r r a from the zone of Didymograptus bifid us, must be 

 separated as a new species. T . s e r r a , thus limited, is in the Deep kill sec- 

 tion restricted to the first two beds (zone with Tetragraptus.) 



In Great Britain the form has long been known by Salter's, Nicholson's, 

 Lapworth's and Hopkinson's investigations. It occurs there in the upper 

 beds of the Middle Skiddaw slates, 

 associated with like forms as in America ; 

 in the Lake district, in south Scotland 

 and in south Wales. ^. ., ^ , , t> • . 



Fig. .jT Tetragraptus serra Brongniart .ip. 

 TO J' ' "j. • 1 X Fragment of branch. Shows the form and inclinii- 



in Scanaina\na it is known to occur tlon of the thecae; and the thick dorsal wall of the 



coenosarcal canal. Deep kill. xi.S 



in Tetragraptus shales in the region of 



Christiana [Brogger], in Skane [Tullberg], West Gothland and Dalecarlia. 



Barrois records it among the fossils from the graptolite schists of Boutoury 



near Cabrieres in southern France, and it was eai'ly found in Victoria, 



Australia. 



Remarl'S. This species exhibits also the strengthening of the branches 

 bv a thickenino- of the dorsal wall of the coenosarcal canal, mentioned in the 

 descriptions of T. quadribrachiatu s and T. amii. As it agrees in 

 nearly all essential featui'es, except the direction of the branches, Avith the 

 latter, there is little doubt that it is derived from that species and marks a 

 further stage in the process of the gradual elevation of the originally depen- 

 dent branches into a reclined position by way of a horizontal disposition. 



The young of this species, which are quite common in graptolite bed 2, 

 possess a characteristic aspect, by having been compressed in such a fashion 

 that two branches appear Xo have a dependent and two a reclined position 

 [pl.n, fig.8]. 



