2 JO NEW YORK STATE MUSEUM 



amphigraptus Lapworth 

 In his valuable paper on an " Improved Classification of the Rhabdo- 

 phora," Lapworth [1873, p. 5 59] has erected and briefly diagnosed the genus 

 Amphigraptus for the reception of a form described by Hall from the shales 

 at the Normanskill as Graptolithus divergens. In the Monograph 

 of British Graptolitcs [pt 3, 1902, p. 121] the following diagnosis of Amphi- 

 graptus is given : 



Polypary rigid, bilaterally subsymmetrical, consisting of two uniserial 

 main stipes, diverging from the sicula at an angle of approximately 180 , 

 which give off regularly or irregularly disposed, rigid, simple or compound 

 secondary branches constituting a more or less radiate polypary. Thecae of 

 the characteristic Lcptograptus type, with low inclination and small amount 

 of overlap. 



It is further added that the secondary branches agree with the main 

 stipes in all essential characters and that they are typically disposed in pairs. 



" The genus Amphigraptus is," according to the Monographers, " some- 

 what rare in British deposits, and has only been found in the Hartfell 

 Shales in the zones of Dicranot>-. clingani and P leu roe. line- 

 aris and is exceedingly rare in the first named zone." Besides the geno- 

 type, A . divergens, a variety of the same and a second species, A . 

 d i s t a n s, are distinguished. 



The genus is also of extremely rare occurrence on this continent, for 

 only two specimens of A. divergens have come to my notice, one the 

 type of the species in the American Museum of Natural History and the 

 other a specimen in the very large collection from the Normanskill shale at 

 Glenmont, now in the State Museum. Besides this, the form described bv 

 Hall as G . multifasciatus may be also brought hither according to 

 the broader diagnosis in the Monograph of British Graptolites which 

 embraces forms with simple and compound secondary branches. 



The paired branching, which is concentrated in the proximal portion of 

 the main stipes and the leptograptid type of the thecae are distinctly shewn 

 in the enlargements here given of the type specimen of the genotype [see 

 text fig. 188, 190]. 



