GUAPTOLITES OF NEW YORK, PART 1 657 



T. quadrihrachiatus in a sandy slate between Defreestville and West 

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

 the Mo7iograp]i 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. serra 

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

 of T . serra from the zone of Didymograptus bifidus, must be 

 separated as a new species. T . serra, 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 fonns as in America; 

 in the Lake district, in south Scotland 

 and in south Wales. ,,, .- n. , . „ • . 



Pi(?. 57 Tetragraptus serra Ilrongniart xp. 



I„ C!„^ j;„„ ^„ Xi. X„ 1,.,„.„« A« „„ Fragment of branch. Shows the form and inclina- 

 n bCanaina\na it is known to occur tlon ot the thecae; ana the thick dorsal wall of the 



ooenosarcal canal. Deep kill. x4.8 



in Tetragraptus shales in the region of 



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



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



near Cabri^res in southern France, and it was early found in Victoria, 



Australia. 



RemarTcs. This species exhibits also the strengthening of the branches 

 by a thickening of the dorsal wall of the coenosarcal canal, mentioned in the 

 descriptions of T. quadribrachiatus and T. amii. As it agrees in 

 nearly all essential features, except the direction of the branches, Avith the 

 latter, there is little doubt that it is deiived 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 to have a dependent and two a reclined position 

 [pl.ll, fig.8]. 



