LITERATURE OF HYDROZOA. 237 



with the Hydrocorallines, and especially with Millepora. These two 

 groups of Stromatoporoids are, however, united by various transi- 

 tional forms, and they possess structural peculiarities of sufficient 

 importance to preclude the reference of the entire series to any exist- 

 ing division of the Hydrozoa. 



As to their general geological distribution, the Stromatoporoids are 

 not certainly known as occurring out of the Ordovician, Silurian, and 

 Devonian formations. Very few forms have yet been recognised in 

 the Ordovician rocks, but the genus Labechia is well represented in 

 strata of this age. The aberrant genus Beatricea is also Ordovician. 

 In the Silurian rocks, Stromatoporoids are exceedingly abundant, 

 often entering largely into the composition of the limestones of this 

 period. The predominant Silurian genus is Clathrodictyon, but the 

 genera Actinostroma, Stromatopora, and Labechia are also represented. 

 It is, however, in the Devonian rocks, and particularly in the Middle 

 Devonian, that the Stromatoporoids attain their maximum develop- 

 ment, the group being represented in strata of this age by numerous 

 species of Actinostroma, Stromatopora, and Stromatoporella, as well 

 as by forms of Idiostroma, Amphipora, &zc. Stromatoporoids have 

 been said to occur in the Carboniferous rocks, but the true nature of 

 these has not as yet been satisfactorily investigated. There are also 

 certain Secondary fossils which, on further examination, may prove 

 to be referable to the present group. 



LITERATURE OF HYDROZOA. 



I. CORYNIDA. 



i. " Fossil Hydractiniae." ' Geological Magazine,' 1872. Airman. 



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., 5 1877. Carter. 



3. " On New Species of Hydractiniidae, Recent and Fossil/' 'Ann. Nat. 



Hist.,' 1878. Carter. 



4. " Description of Parkeria and Loftusia." ' Phil. Trans.,' 1869. W. 



B. Carpenter and H. B. Brady. 



5. " On the Structure and Affinities of the Genus Parkeria." ' Annals 



Nat. Hist.,' 1888. Nicholson. 



6. " On certain anomalous Organisms which are concerned in the for- 



mation of some of the Palaeozoic Limestones." (Mitcheldeania 

 and Solenopora.) ' Geol. Magazine,' 1888. Nicholson. 



7. " Ueber fossile Hydrozoen aus der Familie der Coryniden." ' Palae- 



ontographica,' Bd. 25, 1877. Steinmann. 



II. Thecaphora and Graptolitoidea. 



8. " Graptolites de Boheme." Barrande. 1850. 



9. " Ueber Graptolithen." Scharenberg. 1851. 



