HISTORY OF RESEARCH. Ixxxiii 



that which is capable of being broken oft' from the common portion." He points 

 out that "the line of junction of the thecae is thickened and projects into the 

 common canal as a rounded shelf or flange." 



As respects the Diplograptidse he states that " the polypary is merely com- 

 posed of two of these monoprionidian polyparies placed back to back," their 

 dorsal walls coalescing into a median septum, " between the two lamina? of which 

 the duplicate virgnla is imbedded." While he regards this as the normal mode of 

 growth, he states in the sequel that in some forms of the Diplograptidas the facts 

 go to show that " the common canal was only partially divided, thus in effect 

 communicating with both rows of thecas as in Betiolites.'''' 



The peculiar characters of the diprionidian forms grouped as Retioloidea leads 

 Lapworth to the view that they form a very distinct group from that of the 

 typical Diplograptide. 



The genus Glossograptus, originally suggested by Emmons for forms like D. 

 spinulosus, Lapworth considers should be retained, as, in addition to the two long 

 thecal spines, there occur " two opposite longitudinal rows of gigantic, isolated spurs 

 developed along the median line of the periderm at right angles with the thecas." 

 A new genus, Lasiograptus, is proposed for such diprionidian forms as have 

 " a connected network " of minute, inosculating threads, " almost completely sur- 

 rounding the polypary." The type species (Lasiograptus costatus) is described but 

 not figured in this paper. 



Three other new genera are described, i. e., Clathrograptus (type C. cuneiformis), 

 Leptograptus (L. flaccidus), and Amphigraptus (A. divergens, Hall). 



Lapworth regards the grouping of the first four families as given in his 

 Analytical Table as the natural one, but that of the other families as " temporary 

 and provisional," especially that of the Diplograptidas. 



In 1873 Salter published an exhaustive Catalogue of the 



Salter J W Cambrian and Silurian Fossils in the Woodwardian Museum 



' A Catalogue of the at Cambridge, illustrated by some figures. The following 



Collection of Cambrian species of Graptolites are figured and briefly described: 



and Silurian Fossils ^ Dictijonema sociale, (2) Graptolithus Hisingeri (sagittarius), 



m e ° ° glc (3) Biplograpsus mucronatus, (4) Phyllograptus angustifolius, 



of the "University of ( 5 ) Didymograpsus gerninus, (6) Tetragrapsus bryonoides, (7) 



Cambridge.' Dichograpsus, sp. Loganograptus, (8) Dendrograpsus furcatule, 



(9) Graptolithus Sedgwiclcii, (10) Rastrites (Graptolithus) con- 



volutus, (11) Rastrites per egrinvs, (12) Viplog. folium, (13) Diplog. pristis, (1 I) Gr. 



ludensis (priodon), (15) Betiolites Geinitzianus. 



1874. In the year 1874 Miller described under the name of 



Miller, S. A., Megalograptus a peculiar " large cylindrical form, not a 



' Cincinnati Quart. , .., , . .. , .,, -, ■, 



, graptohte, bearing Ironds with spmosc processes, ana covered 



34,3 with cellular openings." 



