>4* 



NEW YORK STATE MUSEUM 



V 



I'M 



which in dimensions [see pi. 24, fig. 4] considerably surpass 

 the figures given by Lapworth. The synrhabdosomes exhibit 

 upward of 50 rhabdosomes — but probably consisted of many 

 more since only the short-stemmed rhabdosomes are retained 

 and broken-off long-stemmed rhabdosomes are extremely com- 

 mon on the slabs — and attain a diameter of 1 5 cm, but probably 

 reached still much larger diameters, for the longest rhabdo- 

 somes, which are also those with the longest free stems, are 



obviously most liable to get lost. Sepa- 

 rate rhabdosomes measuring over 10 cm 

 (without the nemacaulus) and nemacauli 

 reaching 7.5 cm have been observed [see 

 pi. 24, fig. 1, 4], indicating a possible 

 combined length of rhabdosome and 

 nemacaulus of 17.5 cm and a diameter 

 of the synrhabdosome of 35 cm or 14 

 inches. With this form the genus Diplo- 

 graptus attained here clearly its maximal 

 development both in size and frequency. 

 The nemacaulus is, in contrast to the 

 size of the rhabdosomes and to the nema- 

 cauli of other varieties, remarkably thin 

 and not surpassing. 1 mm in width. Its 

 extreme thinness in this, the largest 

 variety, is the more remarkable since the 

 stoutness of the nemacaulus ol 1). foli- 

 a c e u s has been pointed out as a note- 

 worthy feature by Professor Lapworth, 

 who added that its broad straplike struct- 

 ure is sugfgfestive of a welt unon one sur- 



^0 



286 



Fi^. 283-87 Diplograptus 

 f c. I i ;i 1 e 11 s vsir. i n c isus [.ap- 

 wortli Fig. 283, 284 Lapworths 

 original figures of Stockport speci- 

 mens ( \ ''' I. I ig. 185 Portions 

 of well preserved mature specimen 

 from Glenmont (x 7). Fig. 286,287 r . . . . , 



Sicularendsof rhabdosomes, show- JaCC OI the I'haiK loSOUH". A IlKlXlimilll 

 ing the sicula and spines (x 5) 



width of 1.5 mm has been recorded for the 



