174 PALAEONTOLOGY OF NBW-VORK. 



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The following species present no positive characters by which they can be identified eithe 



as bryozoa or true corals, except in their mode of growth and general appearance. They have 

 usually been referred to Gorgonia, but there are really no characters visible by which such 

 reference can be made. 



Genus DICTYONEMA {nov. gen.). 

 [Gr. 61XTUOV, rete, and vj(*a, filujn.] 



Frond circular or flabelliform, composed of slender radiating branches which frequently 

 bifurcate as they extend towards the margin ; branches and subdivisions united laterally by fine 

 transverse dissepiments ; branches impressed with deep strise or grooves, producing indentations 

 that sometimes have an elongated rhomboidal ibrm ; axis subcalcareous with a corneous exterior. 



The general structure of this coral is very similar to Fenestella, in its diverging bifurcating 

 branches with transverse dissepiments. The branches appear like flattened black threads united 

 laterally by finer ones, leaving quadrangular interstices. One species forms large circular fronds 

 sometimes a foot in diameter, while the other has been seen only in flabellate forms. The 

 branches of these corals consist of a black film enveloping a semi-calcareous or corneous in- 

 terior, and they have the appearance and texture of Graptolites, to which they are doubtless 

 closely allied. A single branch, where the lateral connexion with others is broken off, can 

 scarcely be distinguished from some species of Graptolites. 



569. 1. DICTYONEMA RETIFORMIS (n.s;).). 



Pl. XL F. Fig. 1 a, b. 

 Gorgonia? retiformis. Geol. Rep. 4th District, p. 116, fig. 1, 1843. 



Frond circular, or expanded cyathiform in its growing state (flattened in its fossil condition) ; 

 branches thin, flat, frequently bifurcating, united laterally by obliquely transverse filaments, 

 leaving oblong quadrangular interstices ; surfaces of branches indented, or intermittingly striated 

 in an oblique direction. 



This species is readily recognized in its more perfect condition by the circular form, compa- 

 ratively broad and flattened branches, which radiate on every side from a centre. The branches 

 do not strictly reticulate, although a cursory examination gives this impression, particularly in 

 fragments where the circular character of the frond and radiating branches are not observable. 

 It is a common species in the shale at Lockport, and fragments are found at nearly all localities 

 of the same rock, though perfect fronds are extremely rare. 



The species can have very little if any true relations with Gorgonia, to w^hich it was 

 previously referred, with doubt, upon the authority of Lonsdale's figures in Murchison's Si- 

 lurian System. The specimens are preserved in calcareous shale, where the most minute and 

 delicate forms of Fenestella and Retepora retain their texture in the most perfect manner. 



