C. Lapworth — On British Graptolites. 559 



developed into a third and central branch. Thec£B o£ the form of 

 those of Pleurograptus. Eadicle and lateral spines usually invisible. 



Example — Leptograptus Jlaccidus, Hall sp. 



Amphigraptus (gen. nov.). (Gr. a/judn, on both sides.) 



Polypary consisting of two principal, compound, slender, mono- 

 prionidian branches, proceeding in opposite directions from the 

 major extremity of a small, inconspicuous sicula. Secondary 

 branches normally simple ; given off from both margins of the 

 principal branches, in the neighbourhood of the initial point, usually 

 in pairs. Thecfe of the form of those of Fleurograptus. Eadicle and 

 lateral spines invisible. 



Example — Amphigr. divergens, Hall sp. 



Section U. — Eetiolotdea. 

 Fam, : Glossograptid^. 



Lasiograpttjs, gen. nov. (Gr, Xdaco^ — hairy, shaggy.) 



Gen. char. — Polypary diprionidian, simple ; with sub-parallel mar- 

 gins; section somewhat concavo-convex. Virgula slender, central. 

 Periderm thickened. ThecEe somewhat resembling those of Clima- 

 cograptus ; separated by distinct and deep " excavations," and having 

 their proximal walls strengthened by a pair of chitinous filaments, 

 which converge at the margin, and are prolonged outwardly as a 

 simple spinous process. This process gives origin to a series of 

 slender filaments, which anastomose with those derived in a similar 

 manner from the processes immediately above and below, and form a 

 row of meshes almost surrounding the polypary. Lateral spurs 

 rarely present. 



Example — Lasio. costatus, sp. nov. — Polypary -I to f of an inch 

 in length — margins converging towards both extremities ; maximum 

 width -L- of an inch, or, inclusive of the extraneous meshes, -i. of an 

 inch. Virgula slightly prolonged distally : Thecfe inclined to 

 the axis of the polypary at an angle of about 45° : outer walls 

 little shorter than the interspaces : apertures apparently situated 

 within the general boundary of the polypary. 



Horiz. : Lower Mofiat Shales (Lower Llandeilo), S. Scotland. 

 Fam. : Eetiolitib^. 



Clathrograptus (Lat. clathrum — a lattice). 



Gen. char. — Polypary diprionidian ; simple ; elongate elliptical in 

 form, or with sub-parallel margins : section square. Periderm 

 reduced to a mere film, which is usually invisible ; supported on a 

 skeleton framework of chitinous threads. Virgula an extremely 

 minute longitudinal filament, forming a portion of the supporting 

 framework. Thecae inclined, of the general form of flattened rect- 

 angular prisms. 



Example — Clathrograptus cuneiformis, sp. nov. Polypary cunei- 

 form ; from ^ to -J of an inch in length ; attaining maximum width of 

 -L- of an inch at its distal end : proximal extremity pointed, destitute 

 of ornamental processes. Virgula excessively slender. Thecse 22 to 

 24 to the inch, making an angle of about 30° with the line of the 

 virgula furnished with short, stiff, apertural spines. 



