C. Lapioorth — On Scottish Monograptidce. 311 



The title Monoyraptus, on the other hand, was proposed for a 

 group of species which are regarded by British palaeontologists as 

 belonging to two distinct genera ; and if it is to be employed at all 

 by them, it must be in the restricted sense in which they presently 

 employ Graptolithus. The title is, however, far more definite than 

 Monoprion, and is, at the same time, in perfect harmony with the 

 principle of nomenclature in the Graptolites in general. 



Guided by these arguments, and by the further consideration that 

 we gain in this way a very convenient and unmistakable title for 

 one of the most important families of the Graptoloidea, the title 

 Monograptiis is employed by Mr. Hopkinson and myself in the sense 

 here advocated. 



6. Characteristics. — The family of the Monograptidis, as originally 

 founded by myself,^ included all those forms of uniserial Rhahdo- 

 pliora at that time recognized, in which the polypary was unilateral. 

 The subsequent discovery of the unilateral and uniserial genus 

 Azygograptus,^ Nich. and Lapw., which cannot be placed here, but 

 must be arranged with Coenograptus, Hall, and its allies among the 

 Leptograptidce ( = Nemagraptidoe of Ho^hinson), necessitates a fresh 

 diagnosis of the family. In all the known monoprionidian Rliahdo- 

 pJiora, with the exception of the Monograptidce, the distal portion of 

 the attached sicula is isolated. Here, on the contrary, it lies back 

 upon, and is affixed to, the dorsal margin of the proximal end of the 

 polypary. The members of the family of the Monograptidcd as 

 thus restricted may therefore be now defined as — 



Unilateral Graptoloidea, in which the sicula is thrown hack 

 upon, and united to, the dorsal margin of the proximal 

 extremity of a simple or compound monoprionidian polypary. 



7. Development. — The sicula of the Monograptidce has been already 

 figured by Herr Eichter ^ under the title of the ''foot.'' In the 

 great majority of the species of the family in which its presence 

 has been recognized, it is of very diminutive size, rarely exceeding 

 one-twentieth of an inch in length. In some forms, however, as in 

 Monograptus gregarius, Lapw., Plate X. Fig. 12c., its length exceeds 

 one-fourth of an inch, and the development of the polypary can be 

 easily followed step by step. In this family the sicula is identical 

 in form with that in the bilateral Graptoloidea, which has been 

 already described.* The polypary originates from a point near the 

 broad end of the sicula ; but, instead of proceeding freely outwards 

 as in the bilateral forms, it grows backwards along the distal 

 portion of the sicula itself, to which it adheres by its dorsal surface, 

 and passing beyond it, is continued onwards in the same general 

 direction. 



As in other families of the Graptoloidea there occur, now and 

 again, remarkable monstrosities, caused by a departure from the 



1 Geol. Mag. Vol. X. p. 555, Tab. I. 



2 Annals and Mag. Nat. Hist. 1875. 



3 Zeitschrift d. Deutsclien Gesellsch. 1871, Taf. v. fig. 1. 



* Geol. Mag. Vol. X. p. 501 ; and Quart. Journal Geol. Soc. vol. xxxi. p. 639. 



