238 BRITISH GRAPTOLITES. 



Figs. L5Y c and d.—Orthograptus trun- commences; both the spines are al)Ollt 1 mm. in 



coins, var. socialis, Lapw. , , , ,, , , , ,. , 



length. All the tnecns are markedly alternate m 

 their arrangement, and though in the obverse aspect- 



there appears to be a septum, it must be incomplete, 

 for it is always invisible in the reverse aspect of the 

 polypary. Many of the thecae show beautiful 



growth lines on their walls. 



Horizon <i ltd Localities. — Upper Hartfell Shales 

 c d (Dicellog. complanatus zone). 



c. Complete specimen on same slab as S. Scutltllltl : Dobb's Linn; Shallocll Mill, etc. 



d. mstai^c^o/'another specimen Ireland: Coalpit Bay, Donaghadee. 



from same locality. AsSOCiateS, etc.— V&T. SOciolls is a COmillOll fossil 



at Dobb's Linn in the fossiliferous band in the Barren Mudstones known as 

 the zone of Dicellograptus complanatus, where it occurs associated with I), compla- 

 natus and Glimacog. miserabilis. It occurs with similar associates in the Girvnn 

 country, and in the North of Ireland, where it is extremely well preserved. 

 Collections. — Sedgwick Museum, Lapworth, and the Authors. 



Diplograptus (Orthograptus) cyperoides, Tornquist. 



1807. Diplograptus cyperoides, Tornquist, Kongl. Fysiogr. Sallsk. i Lund Handl., vol. viii, p. 16, 

 pi. ii, figs. 30—32. 



Polypary very small and slender, rarely exceeding 7 mm. in length, and having 



a maximum breadth of 1 mm. Sicula very long. Thecae twelve in 10 mm. ; 



narrow tubes, with slight overlap ; apertural margins slightly undulate, 



occupying about one quarter of total width in bi-profile view. 



Description. — The polypary is very small, but is characterised by the relatively 



Figs. 158 a and b.-Orihograptus great length of the sicula, which may reach 3 mm. 



cyperoides, Tomq. Th< -,i ig gligll tly i onger than any theca subsequently 



developed ; it has a length of 2 mm., and, originating 



near the aperture of the sicula, grows straight 



// ui) ward and outward; th. I 2 grows from it in such a 



manner that the sicula is left free for a considerable 



Y, fraction of its length on one side. The aperture of 



b tli. 3 1 is on a level with the apex of the sicula. 



a. r-roximai end, obverse aspect, show- The remaining theca?, usually five or six in each 



Lng long sicula. Dobb's Linn, Long 



Cliff; liirkhiii Shales (zone of m. thecal series, have an average length of 1 mm., 



gregarius) . Coll. Elles. . , 



b. Specimen in relief, showing complete are seen in bi-profile view to have an overlap of 



but shorter sicula, and septal groove. , . , , ,„ . . , , 



Llanystomdwy, near Criccieth; OHO third to Olie halt their length, ai)(l to haA'C 



Llandovery Beds (zone of M.fimbri- , ■• v i j.n i mi 



atus). Coil. Fearnsides. their apertural margins slightly everted, lliere 



