438 



BRITISH GRAPTOLITES. 



Monograptus turriculatus (Barrande). Plate XL1V, figs. 4 a — e. 



1850. Graptolithus turriculatus, Barrande, G-rapt. de Bohenie, p. 56, pi. iv, figs. 7 — 11. 



1868. Graptolites turriculatus, Nicholson, Quart. Journ. Geol. Soc, vol. xxiv, p. 542, pi. xx, figs. 



29, 30. 

 1876. Monograptus turriculatus, Lap worth, Geol. Mng. [2], vol. iii, p. 359, pi. xiii, figs. 6 a — c. 

 1881. Monograptus turriculatus, Linnarsson, Geol F6ren. i Stockh. Forhandl., v, p. 518. pi. xxii, figs. 



13-18. 

 1892. Monograptus turriculatus, Tornquist, Siljansomrad. Grapt., ii, p. 38, pi. iii, figs. 24 — 26. 

 1897. Monograptus turriculatus, Perner, Grapt. de Boheme, p. 15, pi. xii, figs. 34 — 38. 



Polypary usually small, coiled in a conical spiral from 1—3 cm. in 

 length, widening from a somewhat slender proximal portion, which forms 

 the apex of the cone, to an average breadth of about 1 mm. (exclusive of 

 spines). Sicula conspicuous. Thecse twelve in 10 mm. of the general type 

 of M. Sedgivickii but apparently with two spines. Overlap increasing to 

 one-half the total length as a maximum. 

 Description. — -The appearance of this species varies very much in different 

 individuals, as the result of compression upon a polypary of such peculiar form. 



The most typical and characteristic 



Figs. :ii»l a- 



c. — Monograptus turriculatus (Barrande). 





\<- 





appearance is that of a symmetrically 

 grown conical spire, but the spire may 

 be unsymmetrically compressed. Not 

 infrequently it is compressed from its 

 apex, and then presents a disc-like 

 appearance not unlike that of M. discus. 

 The sicula, which is curved, 

 measures 1*2 mm., and reaches nearly 

 to the top of th. 2. 



The early thecaa are all small and 

 possess spined apertural margins, and 

 in the more distal thecal these spines 

 measure 2 mm. or more in length. 

 Some of the thecas, if not all, seem to 

 have two spines, for when compressed 

 one appears to come from the back and 

 one rom the front of the theca. 

 Affinities. — In its usual state of preservation the shape of Monog. turriculatus 

 is unique, and in its characteristic habit it could not be confused with any other 

 graptolite ; when compressed, however, from the apex of the cone it presents a 

 superficial resemblance to M. discus, but may be easily distinguished by the spined 

 nature of the thecas. 



a. Complete specimen, showing conspicuous sicula. River 



Twymyn, Llanbrynmair ; Brynmair Beds. Coll. Wood. 



b. Thee.e, showing apertural spines. Meigle Quarry, S. 



Scotland : Gala Heds. Coll. Lapworth. 



c. Specimen, showing the two apertural spines. Enlarge- 



ment of part of PI. XL1V, fig. 4 e. 



