142 BRITISH GRAPTOLITES. 



but the more complete specimeus rarely exceed 3 cm. in length, and still smaller 

 forms are of more frequent occurrence. As a general rule the stipes are straight 

 and rigid proximally, but some of the longer specimens take on a slight concave or 

 convex curvature towards their distal extremities. Occasionally the proximal 

 parts of the stipes run almost parallel to each other. At their origin the stipes 

 measure 7 mm. in breadth, but they widen quickly up to 1—1-2 mm., a width 

 which is subsequently maintained. 



The sicula is somewhat broad; it commonly only appears as a slight node 

 between the dorsal walls of the stipes, but when perfect has a length of about 

 1-3 mm; its apertural spine is clearly visible on the ventral margin. 

 Theca l 1 originates basally and grows out at first horizontally, but bends 

 Fms. 86 a a.ndi. -piceiio graptus anoeps, ab ™P% upward in the region of the aperture 



which thus opens almost at right angles to the 

 original direction of growth. Th. I 2 develops from 

 th. I 1 in a similar manner, but is slightly longer, and 

 hence the sicula often appears to be situated un- 

 symmetrically with regard to the two stipes. Where 

 the upAvard growth of th. I 1 and th. I 2 commences 

 a small spine is given off, but this is only visible 

 in very well preserved specimens. The whole 

 ' C D^bK e Lin^S structure of the proximal end perhaps approaches 



6. Primal end (obverse view), showing m0re nearl 7 tlial1 that ° f an y otller Species of 



oi C ^xx!fio- E 3! ; ai,8 ' ement ° f part Dicellograptus to the type perfected in the Diplo- 

 graptidaa. 



All the thecce which are developed after th. 2 1 and th. 2 2 arise from the 

 theca immediately underlying. In their general form they closely resemble 

 those of a typical Climacograptux, having an approximately straight ventral wall. 

 A small mesial spine is given off from about the middle of this wall on the more 

 proximal thecge, and where this spine is conspicuous its base gives a marked 

 curvature to the ventral margins of the theca. Where, however, the spines are 

 wanting or invisible the thecal wall is seen to be normally straight. Spines have 

 been detected up to the fifteenth theca from the proximal extremity in British 

 specimens, and Tornquist records their existence on all the distal thecas, but they 

 are certainly more conspicuous proximally. Each theca is 1*5 mm. long and over- 

 laps for one third to one half of that length. The apertural excavation is large and 

 occupies half the width of the stipe, and about one third of the length of the free 

 outer wall of the theca. 



Affinities. — D. anceps may be separated at sight from all other Dicelloqra/pti (J) 

 by its narrow axil ; (2) by its inconspicuous sicula, more or less concealed by the 

 four proximal thecaa ; (3) and by the straight free outer walls of its thecse, those 

 nearest the proximal end bearing small projecting spines. 



