906 PALAEONTOLOGY OF NEW-YORK. 



that this praptolite was composed of four semielliptical parts joined at their straight 

 sides, and projecting rectangularly to each other; presenting on each of the four 

 margins a series of serrattires, which, penetrating towards the centre, w>re all united 

 in a common canal, and all sustained upon a simple radicle. 



Under this genus have been described the following species from the Canadian 

 collection : 



PhYLLOGRAPTUS TYPCS, p. ILICIFOLIUS, p. ANGUSTIFOLIUS, End P. SIMILIS. 



While these discoveries have been made in Canada, giving us for the 

 first time a correct knowledge of the mode of growth and the varying 

 forms of these bodies, I have not neglected opportunities of increasing 

 our knowledge of these fossils from localities within my reach. The lo- 

 cality of graptolites near Albany has heretofore furnished several species, 

 which, now that we know better their original forms, offer additional 

 information, and become of greater interest both in their zoological and 

 geographical relations. 



At this locality, some specimens have been obtained which show 

 apparently the mode of reproduction in this family of animals, which is 

 more similar to the hydroid polyps than to the Bryozoa*. 



The specimens in which this feature has been observed, first show a 

 Blight swelling or vesicle proceeding from the axils of the serratures : 

 this vesicle, which in the beginning is barely perceptible beyond the out- 

 lines of the margin, swells and becomes elongated, the extremity finally 

 much inflated, and the base of the footstalk extended and attenuated. As 

 this process of development goes on, the sac or inflated portion curves 

 downwards, and finally becomes ruptured or dehiscent on the lower side 

 near the extremity. At this period, and sometimes previously, the sac, 

 which appears to be an extremely thin membrane and almost without 

 substance, shows one or two elongated fibres, like the central midrib or 

 the marginal longitudinal fibre of the graptolites. At a more advanced 

 stage the substance of the sac gradually disappears, apparently by de- 

 composition, leaving the slender fibre still attached for some time to the 

 axil of the serrature. 



* This notice was read at the meeting of the American Association for the Advancement of Science at 

 Baltimore In 1868, accompanied also by references to the Canadian griptolitcs. 



