468 NEW YORK STATE MUSEITM 



rocks ddded in Hall's most important work on this subject, GraptoUtes of 

 tlie Qiiebec Group [1865]. In this memoir, which is classical for the study of 

 American graptolites, all the evidence collected up to that time by Barrande, 

 Geinitz, Hall and other observers, is critically discussed, and the compound 

 form of numerous Dichograptidae and the presence of a central disk, in con- 

 trast to the fragmentary material then known in Europe, fully set forth. 

 Further, three new graptolites from the U tica shale of Lake St John, Canada, 

 among these a compound Retiograptus, are described in a supplement. 



As Hall's conception of the graptolites, laid down in this work, was 

 adopted generally and finds, on the whole, expression in the textbooks still in 

 use, though recent investigations have greatly modified it, we here cite his most 

 important views. He states that it is shown, both from analogies and from 

 the mode of development or reproduction exhibited in some of the species,^ 

 that they are true " Polypi," and comparable to Sertularia and Plumularia. He 

 clearly recognized the common canal as connecting the denticles (" calycles " 

 or " cellules ") of the stipes. The calycles were properly conceived as the 

 habitations of zooids (polypi). But it was held with Barrande that all " grap- 

 tolites proper " (this excludes Dictyonema etc.) had a solid axis, a view which, 

 as we shall explain later on [p. 487], has been disproved ; and that the saw- 

 like, theciferous stipes were united by connecting processes which " were 

 always destitute of cellules," and were therefore " f unicles." Recent investi- 

 gations have demonstrated the composition of these connecting processes of 



iThis refers to the discovery in the Normanskill shale in the neigliborhood of 

 Albany, of a Diplograptus with peculiar, apparently saclike appendages of the stipes, 

 which he compared to the gonangia of the U^'drozoa. A note on this discovery had been 

 published, together with the description of two new species from the Normanskill shale, 

 in the 12tli annual report of the New York State Cabinet [1859] and reprinted, 

 augmented by the descriptions of live more species and several new genera from the same 

 shales, in the Paleontology of New York, volume 3, supplement. As the writer has demon- 

 strated elsewhere [1895], the siculae of Diplograptus are produced in sacs, encircling the 

 central disk of the compound fronds, and the appendages described by Hall bad probably 

 some other function. 



