On the structure and affinities of the genus Monticulipora and its sub-genera, with critical descriptions of illustrative species . in the Hudson River Group; at the same time that I re-gard the former as the type of the species. The chief differ-ences between these two forms may be advantageously addedhere, their chief points of agreement having been previouslynoticed. The typical exahiple from the Trenton Limestone(fig. 32, a) is a large undulated and folded mass, with a maxi-mum diameter of about four inches, and a heifrht of about S UB- GENUS MONO TR YPA. 173 two inches, the calice-bearing
On the structure and affinities of the genus Monticulipora and its sub-genera, with critical descriptions of illustrative species . in the Hudson River Group; at the same time that I re-gard the former as the type of the species. The chief differ-ences between these two forms may be advantageously addedhere, their chief points of agreement having been previouslynoticed. The typical exahiple from the Trenton Limestone(fig. 32, a) is a large undulated and folded mass, with a maxi-mum diameter of about four inches, and a heifrht of about S UB- GENUS MONO TR YPA. 173 two inches, the calice-bearing upper surface being nearly sections (fig. 32, r.) show that the ordinary coralliteshave an average diameter of from i-7oth to i-5oth inch, whileat the angles of junction of these are often small angular tubesof I-300th inch diameter or less. The angles of junction ofadjoining corallites are often slightly thickened, though neverconspicuously so, and the corallites are otherwise uniformlythin-walled. On the other hand, the specimens from the Hudson RiverGroup (fig. 33, a) form rounded or irregularly spheroidal. Fig- 33- — A, A specimen of MonticuHpora iimiidata, Nicli., from tlie Hudson River Group ofCanada, of the natural size, partly broken away on one side ; B, Tangential section of thesame, enlarged eighteen times ; c, Vertical section of the same, similarly enlarged, show-ing the wavy walls and the remote tabula;. masses, generally from an inch to an inch and a half in dia-meter, and sometimes growing round the stem of a of my specimens exhibit an unworn surface. Tangen-tial sections (fig. i,^, b) show that the ordinary corallites havean average diameter of from i-QOth to i-6oth of an inch, andthat they are therefore, upon the whole, slightly smaller Intheir dimensions than is the case with the correspondingcorallites in the Trenton Limestone specimens. A consider-able number of small angular corallites, of an average diameterof I-300th inch,
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Keywords: ., bookauthornicholso, bookcentury1800, bookdecade1880, bookyear1881
