232 



CHAPTER XIL* 



DEVONIAN FOSSILS. 



Steganodictyum (M'Coy), n. g. 

 Etym. ^T€yavo<i, covered, and BUrvov, a network. 



Gen. Char. Polymorphous, forming either narrow, rounded, 

 branch-like masses, or extended into thin, flat, foliaceous ex- 

 pansions ; the interior of all the forms composed of rather 

 large, irregular, polygonal or subhexagonal cells, the three 

 dimensions of which are approximately equal (commonly about 

 half a line in diameter), which become rapidly smaller towards 

 the exterior, blending with the dense covering of the surface, 

 which is variously sculptured with close waving lines, tuber- 

 cles or costse according to the species ; surface dense, forami- 

 nated by the contracted, rather distant openings of the small 

 cell-mouths. 



These curious zoophytes abound in a particular layer of dark 

 Devonian schist near Polperro on the coast of Cornwall, 

 and are the bodies which have been taken for fossil fishes by 

 all previous observers— the thick reticulated fragments being 

 quoted as " bones of Asterolepis -/' flat sculptured portions 

 being taken for the scaly parts of various fishes, and the midribs 

 of some of the fronds being supposed to be " Ichthyodorulites, 

 as DiplacanthuSf Ctenacanthus, and Upper Silurian species of 

 Onchus." The supposed correctness of the latter identifications 

 induced Sir R. Murchison to colour the part of the Cornish 

 coast where these fossils occur as Upper Silurian, in his last map 

 of that region. I first examined a good suite of these supposed 

 Cornish fossil fishes at the Museum of Economic Geology, Jer- 

 myn Street, in company with Prof. Sedgwick last July, and at 

 once demonstrated their true nature to Mr. Salter, who was kind 

 enough to allow me to examine them closely. I subsequently 

 examined the originally figured and described specimens at the 

 Museums of Penzance and Truro, and finally visited the loca- 

 lities where they are found, and procured numerous specimens, 

 now in the Geological Museum at Cambridge, as well as examined 



* The species in this chapter date from the 'Annals ' for Dec. 1851. 



