204 BRITISH GRAPTOLITES. 



The sicula is visible for about 1 mm. of its length. Th. I 1 originates at 

 a point about 05 mm. above its aperture, and grows down to the level of the 

 aperture, and then upward and outward, so that the aperture is on a level with 

 the point of origin ; th. I 2 grows horizontally across the back of the sicula, which 



is thus scarcely visible in the reverse aspect of the 

 Fi«. 134c— ciimacograptus tnbuiiferus, polypary. Short spines arising from the outer 



Lapw. 



walls of th. I 1 and th. I 2 just below their apertures 

 are occasionally visible. 



The thecae have an average length of 2 mm. in 

 the distal portions of the polypary, but in the 

 proximal region they do not exceed 1 mm. in 

 extent; the overlap is approximately one-third. 

 The apertural margins, when seen in true profile, 

 occupy one-fourth of the breadth of the polypary 

 c Distal theca;. Enlargement of part at the proximal end, but distally only about 



of specimen on same slab as Pig. 



136 a. one-sixth. 



Affinities. — -The very gradual increase in width 

 and the broad flattened virgular tube constitute the characteristic features whereby 

 Gl. tubuliferus may be separated from any other known form of Olimacograptus. 



Horizon and Localities. — Lower Hartfell Shales (zones of Bicranog. Olingani 

 and Pleurog. linearis). 



8. Scotland : Dobb's Linn ; Hartfell Spa ; Belcraig Burn ; Mount Benger 

 Burn ; Whitehouse, Ardmillan Shore ; Myoch Bay. Ireland : Carnalea. 



Associates, etc. — Gl. tubuliferus is a fairly common fossil in the zone of Pleurog. 

 linearis of S. Scotland, but it is rare in the zone of Bicranog. Olingani. It is 

 generally found in association with Pleurog. linearis and Gl. styloidens. 



Collections. — Sedgwick Museum, Lap worth, and the Authors. 



Olimacograptus latus, sp. nov. Plate XXVII, fig. 3 a — h. 



Polypary from 2 to 3 cm. or more in length, widening quickly from 1 mm. at 

 its origin to 2 mm., and then more gradually till the maximum of 2*5 mm. 

 is attained. Sicula visible for 0'5 mm. of length. Virgella 1 mm. in extent. 

 Thecae thirteen to ten in 10 mm., basal ones adorned with spines, markedly 

 alternate at proximal end, free edge slightly inclined, average length 

 1-5 mm., overlapping half of it ; apertural margin slightly introverted, lying 

 within deep and approximately semicircular excavations which occupy one- 

 fourth to one-fifth of the breadth of the polypary. 



