284 • Report of the State Geologist. 



later on (in the second volume), in Synthecium elegans, AUm., a 

 form from I^ew Zealand which stands apart from all other 

 Hydrozoa in bearing the gonangia upon peduncles springing 

 from within the hydrothecse, and these hydrothecse do not differ 

 in a single point from the others. 



A highly interesting form has been described by G. Holm * 

 in Dictyonema cervicorne, bearing, alternately on the two sides 

 of hay-forklike spines, cup-shaped bodies, "by thecse," which the 

 author supposes to have been gonangia. The regularity of their 

 distribution on the thecse and the complete development 

 of the by-thecae bearing thecas, are not quite in accordance 

 with the appearance of the recent gonangia and seem to me to 

 be rather suggestive of a comparison with the nematophores or 

 nematocalyces of the Plumularid^. These latter appendages, to 

 which AUmann refers all the thecae of Graptolites, are mostly 

 tube or cup-shaped offsets of the thecae, containing a sarcode 

 mass which can extend itself in the form of single or branched 

 processes. The latter are, as their thread cells indicate, adapted 

 to catching food for the colony. 



The Sicula. 



Professor Hall succeeded in finding the embryo shells, or siculae, 

 as they have been called by Mcholson, not only detached but also 

 in connection with the rhabdosome. They have been found in 

 very widely separated spots, sometimes covering the rocks in 

 enormous multitudes. I, too, have obtained slabs densely cov- 

 ered with siculae and various young stages of D. jpristis^ Hall, 

 while I have only one slab with free siculae of D. Ruedemanni ; 

 these tiny fossils evading detection in the field, although they can 

 be easily seen at the ends of the rhabdosomas, and sometimes 

 even within the gonangia. (PL II, fig. 4.) 



Hall's description of these embryos was so complete and his 

 interpretation of their nature obviously so correct, that both 

 have been only confirmed by later investigations. He saw 

 them, when fiattened upon the rock, as a prolonged triangular 

 film, containing a very fine rod, the virgula. Their real form 

 he supposed to be that of a conical sac. He regarded them as 



* Gotlands Graptoliter. Bighang K. Vet. Akad. Handl. Bd. 16, Af d. 4, No. 7. 



See also : Review by R. R. Gurley In The American Geologist, July number, 1891, p. 35. 



