474 NEW YORK STATE MUSEUM 



of such a funicle has also changed in the last years. And finally he showed in 

 several forms the presence of a disklike expansion of the proximal portion, 

 for which he introduced the term "central disk." 



In the succeeding years discussions of several genera appeared, viz of 

 Didymograptus and Climacograptus by Nicholson [1867, 1870], and of 

 Dicranograptus, Dicellograptus and Diplograptus by Hophinson [1870, 1871]. 



The year 1872 brought the valuable publications of Allman, namely his 

 Monograph of the Gymnohlastic Hydroids, which contains a chapter on the 

 graptolites, and his treatise On the Morphology and Affinities of the GraptoUtes. 

 We shall have occasion to notice his views in greater detail in succeeding 

 chapters, and, therefore, mention here but the most important inferences. 

 AUman holds that the presence of the virgula, or " solid axis," the fact which 

 most obviously opposes itself to an acceptance of the hydroid affinities of the 

 graptolites, though an extremely exceptional structure, can hardly be regarded 

 as offering an insurmountable obstacle to the admission of the graptolites into 

 immediate relation with the Hydroidea, in consideration of a solitary genus, 

 Rhabdopleura, with a similar rod among the bryozoans. The calycles of the 

 graptolite, he compares, on account of their uninterrupted internal passage 

 into the common canal, with the nematophores of the Plumularidae, and the 

 supposed capsulelike bodies, described by Nicholson and Hophinson as 

 gonangia or gonophores, he believes to have had but accidental connection 

 with the graptolites. He is inclined to consider the graptolites "a very 

 aberrant hydrozoal group having manifest affinities with the Hydrozoa." 



While the exploitation of new graptolite fields in southern Scotland 

 \_HopJcinson 1872, Lapiuorth 1872], in Shropshire [Hophinson 1873], in the 

 Hartz [Lossen 1874] was taken up with energy, Lapworth began the 

 systematic work on the distribution and classification of the British graptolites, 

 which has furnished the basis for our present correlations of the graptolite 

 horizons and for the systematic arrangement of the multitude of forms. In 

 his paper, " On an Improved Classification of the Rhabdophora," he pointed 

 out the development of the colonies from a " germ," called by him the " sicula," 



