314 C. Lapworth — On Scottish Monograptldcp. 



line of the periderm, stout at tlieir bases, and narrowing above ; 

 about one-fifth of an inch in length, and the same distance apart. 



All who have hitherto noticed this form have assigned it to 

 Rastrites Lmncei. Barrande gives figures of two examples of that 

 species {Graptolites de Boheme, plate iv. figs. 2 and 3). "We may 

 safely refer the smaller of his examples (fig. 3) to Bas. peregrinus, as 

 it is identical with many of our Scotch specimens. His larger and 

 typical example (fig. 2) — the drawing of which is reproduced here, 

 Plate X. Fig. 3, for comparison — appears to be clearly distinct from 

 any British form yet discovered. Its thecse are nearly one-third of 

 an inch in length, and more than twice as long as the interspaces. 

 Tn Bastrites distans they have only about half that extent, and the 

 lengths of both thecae and interspaces are identical. 



Professor Geinitz figures what seems to be a variety of this 

 species (Die Graptolithen, Taf. v. figs. 16 and 17), in which the 

 hydrothecse are much closer and shorter. It slightly resembles 

 Has. peregrinus, var. hyhridus, and may conveniently be termed var. 

 ahhreviatus. It is figured by Mr. Carruthers from the Moffat Shales, 

 Geol. Mag. 1868, Plate V. Fig. 15. 



Locality. — Rastrites distans is a very rare fossil in the highest beds 

 of the Birkhill Shales at Mountbenger, Craigmichan, Glenkiln and 

 Tushielaw ; and in the Gala Group at Elwand Water, Meigle, 

 Caddonhead, etc. 



4. Eastrites capillaris, Carr. Plate X. Figs. 4 and 4&. 



Bastrites capiUaris, Carruthers; Geol. Mag. 1868, Plate V. 

 Fig. 16. 



I have refigured this species, as Mr. Carruthers' original figure 

 gives a very inadequate idea of its appearance. It more nearly 

 resembles a variety of Monogr. attenuatus (Plate X. Fig. 9 c), which is 

 met with upon the same horizon, and is frequently confounded with it. 



Locality . — Rastrites capiUaris occurs rarely in a single zone near 

 the summit of the Birkhill Shales at Riskinhope Burn, March Burn, 

 Dobbs Linn, Belcraig Linn, Duffkinnel, etc. 



§ III. — Genus MoNOGRAPTUS, Geinitz. 

 Graptolithus or Graptolites, Auct. ; Monoprion, Barrande. 



There are some striking distinctions in the form and disposition 

 of the hydrothec^ in this genus. In all the remaining families of 

 the Graptoloidea, these characters are so stable that they are 

 unerring guides to the systematic position of any polypiferous 

 fragment. Here also they are of paramount importance ; as they 

 enable us to arrange the Monograpti into several well-marked 

 assemblages, in each of which these characters are practically 

 identical. The various divisions thus constituted are each made up 

 of closely allied species, which conveniently admit of being grouped 

 around a special form which is regarded as the type. 



The polypary also varies greatly in its general appearance. 

 Sometimes it is quite straight throughout the whole of its extent 

 (M. colonus, Barr.). Sometimes it forms a plane spiral (M. involutus) 

 or one more or less helicoid {M. turriculatus, Barr.). In the 



