174 CCELENTERATA. 



shape, and destitute of a mouth. The cavities of the zooids 

 are placed in communication with one another by a complex 

 system of canals, ramifying in the ccenosarcal skeleton ; and 

 the true Hydrozoal character of these coral-like forms is 

 shown by the fact that the reproductive organs are situated 

 outside the bodies of the ordinary zooids, being in the 

 form of fixed sporosacs developed within sac-like cavities 

 ("ampullse") in the skeleton (fig. 66, B), which at certain 

 periods communicate with the exterior by minute pores. 



LITERATURE. 



[The following are some of the more important works and memoirs 

 which may be consulted by the student of the fossil Hydrozoa.~\ 



CORYNIDA. 



1. "Fossil Hydractiniae." < Geological Magazine,' 1872. Allman. 



2. " On the close Relationship of Hydractinia, Parkeria and Stromato- 



pora, with descriptions of new species of the former, both recent 

 and fossil." ' Annals Nat. Hist.,' 1877. Carter. 



3. "On Paleeocoryne." 'Phil. Trans.,' 1869. Martin Duncan and 



Jenkins. 



GRAPTOLITID.E. 



4. " Graptolites de Boheme." Barrande. 1850. 



5. " Ueber Graptolithen." Scharenberg. 1851. 



6. "Die Graptolithen." * Versteinerungen der Grauwacken-forma- 



tion.' Geinitz. 1852. 



7. " Graptolites of the Quebec Series." ' Descript. of Canadian Organic 



Remains.' Decade ii. Hall. 1865. 



8. " British Graptolites." ' Siluria,' 4th Edition, Appendix. Car- 



ruthers. 1867. 



9. " Monograph of the British Graptolitidse." Part i., General Intro- 



duction. Nicholson. 1872. 



10. " Morphology and Affinities of Graptolites." ' Annals Nat. Hist.,' 



1872. Allman. 



11. " Notes on British Graptolites." ' Geol. Mag.,' 1873. Lapworth. 



HYDROCORALLIN.E. 



12. "Contributions to the Natural History of the United States." 



Louis Agassiz. (The animal of Millepora is figured, vol. iii., 

 pi. xv., and the genus is referred to the Hydrozoa.) 



13. " Observations critiques sur la classification des Polypiers paleo- 



zoiques." Compt. Rend. t. Ixxx., 1875. Dollfus. 



