TRENTON FOSSILS. 289 



mined species of Delthyris ; of acephalous mollusks, Tellinomya levata (Hall), T. nasuta 

 (Hall), an undetermined species of Modiolopsis, and Ambonyclna undata (Con); of Gastcro- 

 pod mollusks, Maclurea Logani (Salter), an undetermined species of euomphaloid shell 

 and Bellerophen bilobatus (Sovverby) ; of cephalopod mollusks, Trocholites ammonius (Con), 

 Orthoceras amplicameratum (Hall), 0. strigatum (Hall), 0. multicameratum (Con), and En- 

 doceras proteiforme (Hall), and of trilobites, Asaphus canalis (Con), Calymene senaria (Con), 

 Ceraurus pleurexanthemus (Green), and Trinucleus concentricus (Hall). 



FOSSIL COKALS. 



Chcetetes lycoperdon. This is a very common species of the Trenton limestone. It often occupies certain 

 layers to the entire exclusion of other fossils; and its branches often cover many yards of surface. The coral 

 is polymorphous, composed of closely aggregated tubes or columns, which diverge gradually from a broad 

 base forming hemispherical masses, or from an imaginary axis producing conicular ramose forms ; tubes 

 minute, fibre-like, traversed by diaphragms; no connecting pores; the coral increases FIG is6 



by sub-divisions of the parent tube, or by the successive addition of lateral or mar- 

 ginal tubes ; exterier envelope sub-membranous. 



This coral appears in various forms; either hemispherical, conical, nearly globular 

 or ramose. The most common form is the hemispherical, greatly resembling that 

 fungus which is commonly called a puff ball. Fig. 186 represents this form. 



This species ranges from the bottom of the Chazy limestone through the whole of 

 the silurian system, and is perhaps introduced again in the Hamilton and Chemung 

 groups. We have found it in Vermont in Shoreham, at Larrabee's Point, at Frost's 

 Landing and the village in Bridport, at the base of Snake Mountain in Addison, in Waltham, Ferrisburgh, 

 McNeil's Point in Charlotte, at various localities in South Hero and Grand Isle, at the north end of Isle 

 La Motte, and at Highgate Springs. 



Tetradium columnaris (Hall.) The genus Tetradium resembles some forms of Cheetetes. Its coralla 

 are massive, consisting of four-sided tubes, and cells with very thin septa or parietes ; cells stellato with 

 four narrow laminse. This genus differs from Seceptaculites in having very thin parietes and four dis- 

 tinct rays within the cells, one to each side. The cells are about half a line in breadth. The tubes, in the 

 different species, vary from one-fourth of a line to nearly a line in breadth : they are very long, and are most 

 frequently united throughout laterally, forming massive coralla, somewhat resembling that of Cheetetes ; 

 sometimes they are united in single intersecting series ; not unfrequently too the tubes are isolated, or 

 only united at irregular intervals. The isolated lubes are nearly quadrangular, the edges being more or less 

 rounded. There is a slight linear depression down the middle of each side externally, opposite the lamellfe. 

 The increase of the coral appears to be by the division of the tubes, the latter spliting sometimes into two 

 cell-tubes, not unfrequently perhaps into four ; opposite lamella? unite and form the new walls .of the 

 young cells, each of which is in the mean time supplied wiih its four rays. 



The following is a description of the species, T. columnare. Coralla massive, hemisperical, or flattened 

 hemispherical, composed of diverging tubes. Cell tubes normally four-sided, but often without very much 

 regularity; the walls of the cells rugose; lamella? very delicate, and generally wan ting; breadth of full grown 

 tubes usually about or but little more than half a line. Transverse septa usually absent. 



This species belongs to the Black River limestone, and was collected at Button Bay Island in Ferrisburgh. 



Columnaria alveolata (Gold). This is the characteristic coral .of the Black River limestone, and its 

 localities have already been specified. It is a hemispherical or irregularly massive coral, consisting of radi- 

 ating, parallel, or diverging tubes; tubes hexagonal (or varying from 5 to 7 sided), striated longitudinally, 

 crossed by transverse dissepiments with vertical radiating lamellre; no communicating pores. 



