358 C. Lapworth — On Scottish Monograptidce. 



Monograptus convolutus, His. As it differs from all the known varieties 

 of that form in the size and straightness of the polypary and the 

 spinose character of its hj'-drothecge, we may more properly regard 

 it with Carruthers^ and Barrande^ as a distinct and well-marked 

 species. 



Locality. — Highest zones of the Birkhill Shales at Dobbs Linn, 

 Moimtbenger, Garple, etc. 



23. Monograptus convolutus, Hisinger, sp. 



Prionotus convolutus, His. ; Lethea Suecica, pi. xxxviii. fig. 7 



Polypary from four to six inches in length, slender, arcuate, or 

 coiled into a flat spiral ; bearing closely-set hydrothecae, in contact 

 only, rising from the convex margin of the periderm at a large 

 angle; sub triangular in form, and having subterminal, unornamented 

 apertures. 



Hisinger' s original example of his Prionotus convolutus was 

 possibly a spirally enrolled form of this Protean species. It is, 

 however, very similar in appearance to the proximal portion of 

 Ci/rtog7'aptus Murchisoni, Carr. ; and it is impossible to identify it 

 with any one of the following forms, which are our only known 

 Scottish varieties. 



Var. (a.) communis. Plate XHI. Figs. 4: a, h. 



Polypary almost straight distally ; proximal extremity sharply 

 incurved. Hydrothecse 25 to 30 to the inch, short, triangular, pointed. 



As a rule the polypary in this variety commences with a strongly 

 recurved proximal portion, varying in length from one-half to a full 

 inch in length. Here the hydrothecee are linear and apparently 

 isolated as in M. triangulatus. As the polypary grows, the thecaa 

 become broader at their bases, till in the adult portion they are 

 truly in contact. Sometimes the denticle is very acute, and is even 

 a little recurved, reminding us of some examples of the lobiferus 

 group. 



Locality. — Common in the higher zones of the Birkhill Shales 

 everywhere. 



Var. (b.) FiMBRiATUS, Nicholson. Plate XIII. Figs. 4 c, d. 



GraptoUtes fimhriatus, Nicholson; Quart. Journ. Geol. Soc. vol. 

 xxiv. plate xx. figs. 3. 4, 5. 



Polypary short, arcuate, with incurved proximal end. Hydrothecae 

 30 to the inch, triangular, with rounded apices. 



The hydrothecae are shorter and broader than in var. communis, 

 and they are much more closely arranged. 



Locality. — A rare fossil ; occurs only in association with the pre- 

 ceding variety. 



Var. (c.) PROTEUS, Barrande. Plate XIII. Figs. 4:e,f. 



Graptolithus proteus, Barrande ; Grapt. de Boheme, plate iv. 



figs. 12, 14, 15. Suess, Bohmische Graptolithen, Taf. ix. figs. 



2, 3. Geinitz, Die Graptolithen, Taf. iv. figs. 8, 14, 26, 27, 



28, 29. 

 1 Geol. Mag. Vol. V. p. 127. ^ Defense de Colonies, part iv. p. 25. 



