NEMAGRAPTUS. 133 



Nemagraptus explanatus (Lapworth). Plate XIX, figs. Ga—c. 



1870. Ccenograptus explanatus, Lapworth, Cat. West. Scott. Foss., pi. iii, fig. G8. 



Main stipes G cm. or more in length and "6 — *8 mm. in width, straight or with 

 slight cnrvatnre, diverging from a conspicuous sicida at 180°, but sub- 

 sequently curving upward and outward so as to include a smaller angle; 

 from the thecal margin (commonly the upper side) one or more straight or 

 slightly curved secondary branches are given off. Thecre eight in 10 mm., 

 inclined at about 10°, about 2 mm. long, six times as long as wide, free two- 

 thirds to three-quarters their length. Apertural margins concave, intro- 

 verted. 

 Description. — In their ultimate direction of growth the main stipes include a 

 widely open angle and grow approximately straight. The secondary branches are 

 comparatively short, not exceeding 2 cm. as a general rule, and also have a uniform 

 width of •() — *8 mm. ; there is commonly one, but occasionally evidence of two on 

 each main stipe, and the first of these is given off at some distance from the 

 sicula. 



The sicula is conspicuous ; it has a length of about 1 mm. The point of origin 

 of the stipe is median, the crossing canal being horizontal ; the apertures of th. 1 x 

 and th. 1 2 are not so distinctly mucronate as in some forms, but the interthecal wall 



developed between the first two thecae on either 



Pig. 81. — Nemaqrajitus explanatus . -. „ , . , . . 



(Lapw.). side of the sicula appears frequently to grow back 



to the wall of the sicula. 



The theca3 are fairly closely set. 

 Distal thecae. Enlargement of part of Affinities. — N. explanatus is characterised by the 



PI. XIX, fig. Cc. " . . 



general tenuity of its stipes, their wide angle of 

 divergence, and the presence of one or more secondary 1 (ranches. From all the 

 Nemagrapti of the N. gracilis group it may be distinguished by its habit. Frag- 

 ments are liable to be confused with fragments of var. pertennis, but may be 

 distinguished by the more numerous thecaa in a given unit of length, and by the 

 presence of secondary branches. 



Horizon and Localities. — Upper Llandeilo (Glenkiln). 



8. Scotland: Belcraig Burn; Glenkiln Burn; Cairn Hill; Craigmichan Scaur; 

 Rein Gill; Hawkwood Burn; Berrybush ; Black Linn, etc. .V. Ireland: Ballygrot. 



Associates, etc. — N. explanatus is a fairly common form in the Glenkiln Shales of 

 S. Scotland, where it occurs associated with Nemag. gracilis, var. surcidaris, Dicranog. 

 ramosus, Lasiograptus, sp., etc. Specimens, including the type, are in Lapworth's 

 collection; there are also a few in the collection of the Geological Survey of 

 Scotland and the Authors. 



