GRAPTOLITES OF NEW YORK, PART 2 483 



Description. Synrhabdosome not observed. Rhabdosome medium 

 sized, attaining a length of 45 mm or more, with rounded sicular extremity 

 which is 1 mm wide; attaining its mature width of 3 + mm very gradually, 

 in a distance of about 15 mm. Last moiety of rhabdosome with parallel 

 maroins. Antisicular extremity truncate. Sicula not observed. Thecae 

 numbering 10 to 12 in 10 mm (25-30 in 1 inch), inclined at an angle of 30", 

 overlapping one half or a little more. . Form of thecae as in L . muc ro- 

 il at us. Outer meshwork also as in latter species, but coarser. 

 Nemacaulus very thin and short. 



Position and localities. In the Normanskill shale at Kenwood and 

 Glenmont near Albany, N. Y. and on Mt Moreno near Hudson. In Great 

 Britain the form is recorded from the Glenkiln shales of Scotland, from 

 Wales and Ireland and Tullberg cites it among the graptolites of the zone 

 with Coenograptus gracilis in Scania. 



Remarks. The differences between L . mucronatus and b i m u - 

 cronatus are largely such of relative dimensions. The writer has there- 

 fore been long in doubt as to the propriety of distinguishing the two forms ; 

 the fact, however, that they rarely associate in the same layer and that the 

 larger and coarser form has the thecae arranged more closely instead of 

 more loosely, as one should expect, gives to the latter a so much more com- 

 pact appearance that confusion between the two is little to be feared. The 

 firmer texture of the periderm in this species finds its expression also in the 

 more frequent preservation of the extrathecal meshwork and of the peri- 

 dermal expansions. It was in examples of this species then referred to 

 Graptolithus whitfieldi that Hall observed the " reproductive 

 sacs." 



Lasiograptus bimucronatus (Nicholson) mut. timidus no v. 



Plate 29, figures 19, 20 



The Utica shale of New York, that of Cincinnati and the Maquoketa 

 shale near Granger contain a peculiar small spinose form which obviously 

 is very rare and has all the appearance of a gerontic mutation of one of the 

 spinose species of the Trenton shales. Its principal characters are its com 



