HISTORY OF RESEARCH. lxi 



genus, to include such forms as possess a " variable number (always more than 

 four) of simple stipes, united centrally at the base by a non-celluliferous stem or 

 funicle." He distinguishes two groups within the limits of the genus: (a) Those 

 typified by D. Logani and D. octobrachiatus, in which the celluliferous stipes are 

 never divided at all; (h) Those like D. flexilis, l>. rigidus and l>. multiplex, in 

 which the celluliferous stipes themselves branch and rebranch repeatedly, hike 

 Hall, he does not regard the disc in the Grraptolite as of generic value, and 

 is inclined to believe that its "homologue is to be found in the 'float' or 

 ' pneumatophore ' of the Physophoridas." The disc seen in Climacog . bicomis and 

 others is probably of the same character, and it "may have been developed only 

 at certain stages of growth, in certain individuals of the species, and probably for 

 certain definite purposes." The species of Diclwgrapsus described are l>. Logani, 

 (o) J>. octobrachiatus and two new forms, (4) JJ. multiplex {Temiwgraptus) and (5) 

 D. reticulatus (Schizograptus) . 



In discussing the genus Biplograpsus, it is noteworthy that Nicholson lays 

 great stress on the importance of observing the character of the base for 

 determining the various species, "forming as it does the most valuable aid to 

 a correct diagnosis." The suggestion thus made has subsequently proved to 

 be of especial value in the discrimination of both genera and species. He divides 

 the Skiddaw Slate species of Biplograpsus by their basal characters into three 

 classes, viz. those having (a) a median radicle, flanked by two lateral processes, 

 which spring from primary cellules on each side {IK bicomis, etc.) ; (li) two 

 primary cellules, greatly elongated, forming with the solid axis a broad tapering 

 "radicle" (l>. cometa, etc.); (c) the base formed by a basal extension of the 

 solid axis beyond the proximal extremity of the frond (D. pristinlformis, etc.). 

 He re-describes Diplog. mucronatus and 1>. antennarius, and re-figures (6) /'. 

 teretiusculus and (7) D. pristiniformis. For P. antennarius and l>. teretiusculus 

 he considers that it would be advisable in future to accept Hall's title of Glimaco- 

 grapsus. 



As regards the genus " Graptolites " or " Graptolithus," as then understood 

 (the Monograptus of later authors) Nicholson states that he is " inclined to think 

 that the genus is not represented" in the Skiddaw Slates, and that the forms 

 ascribed to it, such as Gr. Sagittarius, Gr. tenuis, and Gr. Nilssoni are in reality 

 fragments only of compound species. This view has been fully justified by 

 subsequent research. A fragmentary branching form is referred by him to 

 (8) Dendrograptus Eallianus, which species he considers is probably identical with 

 D. furcatula, Salter. 



A new form (9) Pleurograpsus (?) vagans is also described and figured. This 

 is not a Pleurograptus, but belongs to the Dichograptidse ; owing, however, to its 

 fragmentary condition it is impossible to refer it with certainty to any known genus 

 of that family. 



