TRIGONOGRAPTUS. 301 



In one specimen spines similar to the basal ones are seen proceeding from 

 a thecal pair situated higher up the polypary. 



Affinities. — G. antennarius may be readily separated from all other Gri/ptograpti 

 by the long, stiff spines at its proximal end ; these are much longer and stouter 

 than those found in Gryptog. tricornis, and the whole character of the polypary is 

 more robust. 



Horizon and Localities. — Upper Skiddaw Slates. 



Lake District : Outerside ; Mungrisedale ; Glenderamakin Valley ; Mosedale 

 Beck, near Troutbeck ; Bannerdale Fell. 



Associates, etc. — G. antennarius is a fairly common fossil in the Upper Skiddaw 

 Slates, associated with Didymog. indentas. It is, however, invariably poorly 

 preserved. 



Collections. — British Museum (Natural History), Sedgwick Museum, Keswick 

 Museum. 



Genus TRIGONOGRAPTUS, Nicholson. 

 1869. Trigonocjrapsus, Nicholson, Ann. Mag. Nat. Hist. [4], vol. iv, p. 232. 



Polypary bilaterally symmetrical, biserial throughout, transverse section 

 concavo-convex or trigonal, ventral edges having the appearance of being 

 even and continuous. 



Tliecse resembling those of Phyllograptus and Betiolites. 



Test thick, membranous, with transverse growth-lines. 



The genus Trigonograptus was founded by Nicholson to include certain 

 Graptolites found in the Skiddaw Slates of the Lake District. The thecae are 

 generally well marked, and appear to be sub-rectangular tubes expanding towards 

 their apertures, and overlapping for the whole of their extent. They not only 

 recall those of Phyllograptus but also those of Betiolites. 



The transverse section of the polypary was probably strongly concavo-convex 

 or even trigonal, and the appearance of the tliecse varies very much in different 

 views. 



Only one species and a variety are known with certainty in the British Isles — 

 Trigonograptus ensiformis and var. lanceolatus. 



Note. — The first recognised species of this genus — Hall's Graptolithus ensi- 

 formis — was regarded by its discoverer as belonging to Betiolites (Barrande) or an 

 allied genus (Hall, ' Grapt. of Quebec Group,' p. 114). This opinion, which is in 

 harmony with certain similarities in outward form and appearance, has naturally 

 led to its being generally assigned to the family of the Retiolitidas (Lapw., ' Geol. 

 Mag.,' 1873, Table, p. 555, and others). Although it must be admitted that our 



