DICELLOGRAPTUS. 



L51 



Figs. 94 a and &. — Dicellograpius Foi 

 chammeri, Geinitz. 



sicula at varying but always large angles (240° — 320°). Thecse ten to eight in 

 10 mm., overlapping for one third to one half their length; free outer wall 

 curved, apertural portion introverted. Aperture opening within a shallow 

 pouch-shaped excavation, which occupies one third the width of the stipe. 

 Description. — The stipes frequently attain a great length, and are straight 

 or slightly curved, their curvature at the proximal end being always convex, 

 though it may become concave distally. They are only - 5 mm. in breadth at their 

 origin, but widen gradually up to 1*2 mm., after which the increase is hardly per- 

 ceptible. The angle of divergence varies within wide limits. 



The sicula is always conspicuous within the axil; it has a length of l - 5 mm. 

 exclusive of the stout apertural spine ; it becomes very slender towards the apex and 



merges gradually into the nema. The earliest 

 thecse, th. 1 l and th. 1 2 , are large, and play a more 

 important part in the formation of the axil than 

 th. 2 1 and th. 2 \ which is unusual; hence too the 

 whole proximal end is decidedly thinner in appear- 

 ance than is generally the case. The axil has a 

 characteristic wide-open appearance, and the lateral 

 spines on th. I 1 and th. I 2 are conspicuous in all 

 good specimens, though, being slender, they are not 

 always discernible in poorly preserved examples. 

 The development of th. 2 1 from th. I 2 is clearly seen ; 

 it grows obliquely upward, then proceeds horizontally 

 outward, and is finally again directed upward ; hence 

 the sigmoid ventral curvature of the thecse in this 

 species is obvious even at this early stage. 

 The mature thecse have an average length of 2 mm., and are free for one third 

 to one half of their extent ; the free part of the outer wall is curved and oblique in 



the typical profile view, but varies very much with 

 the direction of compression, being sometimes almost 

 straight and sometimes even crenulate in appear- 

 ance. A few proximal thecse, and occasionally even 

 some of the distal thecse exhibit mesial spines. The 

 aperture is always introverted, and opens wholly 

 within the ventral margin of the stipe, in a narrow 

 pouch-shaped excavation. This is usually clearly 

 seen ; occasionally, however, it is almost completely 

 filled by the thecal aperture and then is discernible 

 merely as an oblique slit. 

 Remarks. — D. Forcharnmeri Avas originally described by Geinitz from the Alum 

 Shales of Uornholm. Judging from his figures (loc. cit, supra) he may have 



20 



Proximal end. Enlargement of part 



of PI. XXII, fig. 1 a. 

 Proximal thecoe with mesial spines. 



Specimen on same slab as fig. 1 c. 



Pigs. 94 c and d. — Dicellograpius Foi 

 chammeri, Geinitz. 



r. Distal thecse, showing varioiis aspects 

 Specimen on same slab as PI. XXII 

 fig. 1 a. 



d. Distal thecae, profile view. Enlarge- 

 ment of part of PI. XXII, fig. 1 c. 



