64 REPORT— 1851. 



believed that the genus will be found common in the Silurian rocks, and will include 

 \y many species now referred to Nucula. It might be called Ctenodonta. Of the same 



"^ family also, a Lyrodesma (a genus with radiating teeth beneath the beak and syn- 

 onymous with Actinodonta, Phillips) is closely allied to a Trenton limestone species. 

 There is a new genus probably belonging to the family Arcacidse, but possessing 

 only two or three anterior teeth ; the collection does not include any Avicxilx. Of 

 the few lamellibranchiate shells none appear quite identical with those from New 

 York ; but, as might be expected, the common Brachiopoda of this locality are those 

 most abundant also in the Trenton limestone. Orthis tricenaria, Conrad, swarms here, 

 as does also Lepfcena filitexta. Hall, a shell verj' like the common L. alternata of the 

 Trenton limestone, but reversed as to the convexity of the respective valves. But the 

 latter shell, so abundant in New York, does not occur here. Airypa hemiplicata. Hall, 

 &nAA. increbrescens are tolerably frequent ; and there are two or three species of Or* 

 this, and some small Terehratulas, which require further examination. 



The Bellerophons, two of which are probably identical with New York species, are 

 those of the lowest or chazy limestone, namely, £. (Bucania) sulcatina, Emmons, and 

 JS. rotundata, Hall. The group to which these two belong is that of which the 

 English B. dilatatus is a familiar type, the whorls scarcely enveloping each other, 

 and the mouth wide and trumpet-shaped. There is however a true Bellerophon so 

 like B. obiectus. PhilL, from the Ludlow rocks of Pembrokeshire, that, but for its 

 treble size, it might be taken for it. 



Perhaps one of the most interesting of the mollusks is a large Cleodora, quite new 

 to America, and not yet described as such from Britain. On attentively comparing 

 the American, Irish and North Welsh specimens of this fine shell, which measures 

 two inches across, I can find only trivial variations. It does not require a new spe- 

 cific name, having been figured from an imperfect specimen as Atrypa transversa by 

 Portlock. It is interesting to find this species (which of course, as a Pteropod, had 

 ready means of migration) in the two countries. There are but few other species 

 identical with those of Great Britain, but I think I recognise Turbo frochleatus, and 

 perhaps T. tritorquatus, M'Coy, as common to the two regions. 



Of the Cephalopoda, the remarkable two-edged Orihoceras, called Gonioceras 

 anceps by Hall, is a Black River limestone species. Cyrtoceras is common, both 

 smooth and ornamented ; C. aimulatiim and C. lamellosum, the same with those of 

 Trenton; Orthoceras arcuo-liraium, bilineatum, and laqueatuni, Hall, are Trenton 

 limestone species ; and lastly, there are two species of Ormoceras, Stokes, the larger 

 of which is in all probabihty 0. tenuifilum. Hall, a species both of the Black River 

 and Trenton beds. 



Schizocrinus nodosus, Hall, of the Trenton limestone, is the common crinoid : its 

 stems are very characteristic. 



Among the corals, one or two species of Slreptolasma, apparently the same as 

 those of New York, and the branched varieties of Favosites lycoperdon , accompany 

 those before mentioned ; and we may here notice the Receptaculites, already de- 

 scribed by Hall, but not I think identical with R. Neptuni of Europe. The fine 

 series brought home by Mr. Logan shows all the structural characters ; — the circular 

 expanded form and cup-like centre, — the surface composed of rhomboidal plates, 

 which cohere by lateral processes, and which are the flattened ends of separate and 

 equidistant columns. Unfortunately the entire structure is replaced by cycloidal 

 silex, but perhaps it will by careful polishing enable us to see if it be really a coral, 

 somewhat of the character of the Tuhiporidce. 



To crown all, these are slabs full of the large Asaphus (Isotelus) yigas, the charac- 

 teristic trilobite of the Trenton rocks. 



Upper Silurian RocJcs. — Ascending the Ottawa to the head of Lake Temiscamang 

 and so crossing the granitic axis of Canada, the first fossiliferous rock that presents 

 itself is of a totally different character to that last described, as stated by Mr. Logan 

 in his Report of Progress for 1845. 



This limestone is weathered like the last ; its siliceous fossils also stand out in bold 

 relief; and one of the most common is the characteristic crinoid of the Trenton lime- 

 stone, Schizocrinus nodosus, at least I believe I am correct in this reference. But along 

 •with this are abundance of Favosites yothlandica, Stromatopora siriatella, Cyatho- 



