474 NEW YORK STATE MUSEUM 



which are here freely illustrated [see pi. 30, 31]. From these specimens we 

 have been able to gather the following" facts : 



Glossograptus whitfieldi does not possess any marginal fila- 

 ments, but only two apertural spines, exactly corresponding to those of 

 G. quadrimucronatus, It is most probably, like the latter, a sim- 

 pler member of the genus Glossograptus. Lapworth's suggestion that 

 Hall's specimens bearing the lateral "reproductive appendages" do not 

 belong to G . whitfieldi is, hence, supported by our material as also by 

 an inspection of Hall's types. 



The specimens of Lasiograptus from the Normanskill shale of New 

 York fall easily into two groups, one of slender rhabdosomes with loosely 

 arranged thecae and one of rapidly widening, broad rhabdosomes with 

 closer arrangement of thecae and hence more compact appearance. The 

 former correspond to L . mucronatus Hall, the latter are mostly bimu- 

 cronate and would hence by this character and the size of the rhabdosomes 

 at once suggest their close relationship or identity with L. bimucro- 

 natus Nicholson [see below, p. 481]. Hall's appendage-bearing forms 

 belong to the latter group. 



In regard to the morphology of Lasiograptus our material leaves id 

 doubt that the organisms grew in synrhabdosomes [see pi. 29], at least in 

 L . mucronatus. The latter species has furnished us several compound 

 colonies in the shale from Glenmont, N. Y. ; .among them one with a well 

 preserved center [sec pi. 31, fig. 3]. 



The structure of the rhabdosome of Lasiograptus is evidently very 

 complicated and can be obtained only by conjecture in our shale material. 



The great majority of the specimens of both species retain only the 

 thecae and short apertural mucros. The thecae are characterized by the 

 long, horizontal apertural margins [see pi. 30, fig. 1, 5, etc.]. The periderm 

 of the thecae is extremely thin and lacks the luster of that of other 

 graptolites, recalling in this feature that of Cryptograptus and Retiolites ; 

 and that of L. mucronatus is evidently still much thinner than that of 

 L. bimucronatus. 



