Transactions. 81 



sea bottom, where those serriated aud curiously formed Zoophytes, 

 named Graptolites, seemed to have swarmed in extraordinary 

 abundance ; and, as far as we at present know, they began life 

 in the Silurian system, lived througliout the whole pei-iod, and 

 died out at the close of that formation. Although their geologi- 

 cal range is not extensive, being confined to these old Silurian 

 rocks, their geographical range is very expansive, being found in 

 the British Isles, Australia, States of Aniei-ica, Canada, and 

 various parts of the continent of Europe. It seems a difficult 

 matter to determine to what class the Graptolitidie belong, some 

 authorities believing that they are nearly related to the Virgu- 

 laria of the present seas, others to the Polyzoa, and otliers to 

 Sertularia or Hydrozoa, because they liave a chitinous or horny 

 exterior, with hydrotheca or cells ; but the Sertularia have no 

 solid axis, neither are the cells overlapping each other like those 

 of the Graptolitidie. Again, the Polyzoa possess a calcareous 

 exterior, and in that case are dissimilar. It was thought at one 

 time that Graptolites attached themselves to the rocks or other 

 objects at the sea bottom, while some observers say they were 

 free-floating. From a number of specimens obtained about two 

 years ago, I am thoroughly convinced that the greatest number 

 were fixed bodies, especially tlie genus Monograptus. In the 

 genera Diplograptus and Didiraograptus, there are numbers of 

 species which have no radical point of attacinnent, so I think we 

 may conclude that they were both fixed and free-Hoating. On 

 the other hand, the Polyzoa, with one exception, Chri^talella, a 

 fresh water species, are all attached to some object, and also the 

 whole of the Sertularia, General Portlock appears to have been 

 the first to suggest definitely that the Graptolites were allied to 

 the Sertulari:u and Plumularia? ; however, all modern observers 

 are now agreed in placing the Graptolites somewhere among the 

 Hydrozoa. 



I think it may be advisable just now, as there may be some of 

 the members present who are unacquainted with the Grapto- 

 litida;, to explain the structure of tiiese interesting Zoophytes, 

 and with which I will be as brief as po.ssible. Unfortunately, 

 they are ratlier small objects, but with the aid of these large 

 drawings, and also this model of a Graptolite, I hope to make 

 the description of them much plainer than by describing the 

 specimens you see on the table. When we describe one w^e 

 describe the whole of the genus Monograptus, the polypery being 



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