47' 



NEW YORK STATE MUSEUM 



where now the periderm of the triangular appendages is fading out (at a in 

 diagram). 



On account of the very different structure of the thecae proper and 

 of their distal parts, we believe that the latter do not simply represent a 

 stronger reduction of the periderm of the distal parts of the original thecae 

 but rather a secondary development. The origin of the latter has probably 

 to be sought, as mentioned before, in the apertural loops of Climaco- 

 graptus retioloides. This latter view seems to be well supported by 

 further observations regarding the appendages which have not yet been 

 recorded here. One of these is that the appendages are much greater in 

 size near the older (sicular) extremity of the rhabdosome and absent or 

 hardly developed at the other end [see Hall's type refigured pi. 29, fig. 

 16]. In other words they lag in their growth far behind that of the thecae. 

 In the last mentioned fio-ure it will be seen that while the thecae at the 

 antisicular end are almost as large as those at the sicular end, the thecal 

 appendages are only indicated there as slight swellings (at a), but grow 

 distinctly in size towards the other end. Besides, the}* are there distinctly 

 thicker in texture than the older and larger appendages and fully bounded 

 by a fiber at their rounded distal ends. All this can not fail to suggest 

 growing saclike appendages as it did to Hall. But if we assume that these 

 distal loops of the thecae are but of later secondary development, it may 

 well be expected that they also lagged behind in time of appearance or in 

 the ontogenetic development of the thecae and of the rhabdosome, as they 

 actually would appear to do in the specimens figured. 1 



Another point bearing on the connection of Lasiograptus and C 1 i m a - 

 cogr. retioloides is the like form of their thecae. A comparison of 

 the figure of the latter species, copied here from Wiman [fig. 50] and iii 

 figure 456 will show at once that the outlines of the thecae of both art' alike 

 and differing from those of other retiolitids and diplograptids, in that the 



1 The specimens are slightly twisted, the sicular moiety being obliquely compressed 

 and the other showing the frontal or ventral aspect, hut this could not possibly affect the 

 preservation of the appendages to the degree here shown. 



