SO NEW YORK STATE MUSEUM 



stage is throughout the animal kingdom uniformly free from spines. But 

 it is in line with this fact that the thin proximal part of the sicula, which 

 does not possess growth lines [sec Mem. 7, text fig. 2 ], never possesses any 

 traces of spines and that especially in such genera as Diplograptus, where 

 the virgella extends into the wall of the sicula, it apparently does not enter 

 this "embryonic" part of the sicula. 



The distal part of the sicula appears for this and other reasons to hold 

 in regard to the proximal part the position of a larval form to the embryo, 

 and it certainly holds this position in regard to the whole colon}', represent- 

 ing its astonepionic growth stage. 



In Cryptograptus tricornis this larval stage alone is for- 

 midably armed with four long needlelike spines, while the succeeding thecae 

 are free from spines, and the profusely occurring, spinose siculae remind 

 one of the long spinose larvae or zoeae of crabs. The spinosity of 

 the latter is due to "cannibalistic selection" according to Yerrill, the 

 larvae preying upon each other and therefore needing this protection. 

 While the tenants of the siculae of Cryptograptus can hardly be con- 

 sidered as having been of sufficiently high organization to be able of 

 such cannibalism, the fact is clear that they, like the siculae of many other 

 forms, were subject to attacks which led to a development of spines not 

 repeated in the succeeding thecae and that these spines partake more of 

 the character of coenogenetic features, and are not directly connected with 

 the phylogenetic history of the genus, a view that also agrees with their 

 presence on the oldest species of the genus. In this case the development 

 of spines could not be held to have been pushed back by tachygenesis into 

 the larval stage. 



b Note on terminal spines of Climacograptus bicornis 

 Perhaps the most striking objects among the Normanskill graptolites, 

 especially those from Glenmont near Albany, are the appendages ol 

 the sicular end in Climacograptus bicornis Hall. They present 

 at first sight an almost bewildering variety of forms and all possible modi- 

 fications of a single; pattern. They all occur in one and the same horizon 



