retiolitim:. 333 



Hallog. mucronatus, alternate, fourteen to twelve in 10 mm. ; ventral 

 processes slender, and united to form a continuous delicate lacinia. 

 Description. — The polypary is invariably short; it attains its maximum breadth 

 almost at once, and maintains it to the distal extremity. 



The thecae are of the same general form as those 

 FlGS ' 21 ° a g arii^^T PtWS mar ' of Hallog. mucronatus, but are of smaller size and 



have a lesser amount of overlap. The ventral pro- 



: , •£>-- cesses arising from the denticle are delicate and 



. F*T flexed, and curve broadly downward to meet those 



' , ;- proceeding from the theca immediately below, the 



major interspaces thus formed being about the same 



length as the width of the central portion of the 



a i polypary. There is distinct evidence of a minor 



a. Proximal end. Dobb's Liim, Hartfeii series of meshes along the outer edge of the lacinia. 



Shales (zone of Dicranog. Clingani). 



Coll. Lapworth. No scopulate processes have been observed in this 



b. Distal thecae, showing lacinia. En- 



largement of part of PI. XXXIV, form. 



Affinities. — This species approaches Neurog. 

 fibratus in the general characters of its thecae and their appendages, but, as already 

 pointed out, is a much smaller form ; the test is thicker and the clathria not nearly 

 so pronounced, while the scopulate processes appear to be wanting. 



Horizon and. Localities. — Lower Bala, Lower Hartfeii (zone of Dicranog. 

 Clingani). 



8. Scotland : Dobb's Linn, Hartfeii Spa, etc. 



Associates, etc. — N. margaritatus occurs in great abundance in the Hartfeii 

 Shales associated with Dicranog. ramosus and Leptograptus fiaccidus in the zone of 

 Dicranog. Clingani. 



Collections. — Lapworth, Geological Survey of Scotland, Swanston, and the 

 Authors. 



Family RETIOLITID^], Lapworth (restricted). 

 1873. Retiolitidie, Lapworth, Geol. Mag., vol. x, table i, p. 555. 



Biserial Graptoloidea with straight polyparies. Thecae of the general Diplo- 

 graptid type. Test represented typically by a complete network of minute 

 meshes supported upon a more or less well-defined skeleton or clathria of 

 stronger filaments. Extraneous processes and lacinia absent or present. 



The characteristic feature of all the forms belonging to this family is the 



nehvorh of delicate chitinous tracer ij (reticula) which, forms the outward visible 



■ covering of the walls of the tliecse, and is attached to the skeleton and overlies the 



