DIPLOGRAPTUS. 



251 



Fios. 171 ob and 6. — Glyptogra/ptus tere- 

 tiusculus (His.). 



Polypary 4 — 6 cm. in length, widening very gradually till maximum breadth 

 of 2 mm. is attained. Sicula of moderate size ; virgella long, stout, and 

 conspicuous; basal thecas with unsymmetrically disposed spines. Thecoa 

 fourteen to ten in 10 mm., of the general Glyptograptus type, sacculate 

 above and impressed below, having a length of 2 mm. and overlapping for 

 one half their extent ; apertural margins slightly undulate. 

 Description. — The polypary may attain a length of 6 cm., but specimens 

 measuring about 8 or 4 cm. are of commoner occurrence than the longer forms. 



In general the specimens from the Welsh Border- 

 land are somewhat narrower than the Swedish types 

 described by Tullberg. Examples, however, are met 

 with in association which agree exactly in their 

 dimensions with those given by him, and there 

 appears to be every gradation between them. 



The proximal end of the polypary is relatively 

 broad, but the proximal thecae are small. The sicula 

 has a length of about 1'5 mm., and the virgella is 

 fully 3 mm. long. Th. I 1 originates near the apex 

 of the sicula and grows distinctly downward before 

 bending round to grow outward and upward. It 

 gives off a short spine close below its aperture. 

 Th. 1~ also stows in a downward direction before 

 turning upward and outward, and carries a distinct 

 sub-apcrtural spine below its slightly everted aper- 

 ture. 



The thecce subsequently developed are all some- 

 what sacculate, with a constriction immediately below 

 the apertural margin in compressed examples. In 

 the reverse bi-profile view they all exhibit gently 

 flowing sigmoid curvature in their ventral walls, and 

 the free edge is but slightly rounded ; they overlap 

 from one third to one half their length. Their 

 apertural margins are often markedly introverted, 

 while in some cases there is also a suggestion of 

 introversion of the whole apertural region. In 

 what appears to be the reverse aspect the exca- 

 vations are also shallow and pouch-shaped, occupying about one fifth of 

 the total breadth of the polypary, but in the obverse aspect the excavation 

 appears more pronounced, the ventral wall more rounded, and the whole 

 appearance nearer that of G. tamariscus. In some views a row of pustules 

 close to the inner angle of the pouch is often shown, apparently due to the COm- 



ci. Proximal end, reverse aspect ; sicnla 

 pressed through and unusually 

 prominent. Enlargement of part 

 of PI. XXXI, fig. 1 a. 



b. Proximal end, normal reverse aspect. 

 Grwern-y-fed -fach, near Builth, 

 Llandeilo Beds. Fraser's Collec- 

 tion. 



Figs. 171 c and d. — Glyptograptus tere- 

 tiusculus (His.). 











•'-'i- 







c and d. — Distal thecse, showing the 

 various appearances they present 

 under compression. Enlargements 

 of part of PI. XXXI, fig. 1 b. 



