CRYPTOGRAPTUS. 



297 



Figs. 200 a — c. — Cryptograptus tricornis 

 (Carrcithers). 



: ; 



; • 





detected, and the position of the thecas themselves can only be inferred from the 

 crenulation of the ventral margin ; the virgella and lateral spines, however, 

 stand out very clearly in this aspect. 



The characters of the proximal end are very 

 obscure in adult specimens, but from young examples, 

 which are fairly abundant, it can be seen that the 

 sicula was very long, being fully 3 mm. in length. 

 Its apertural edge is thickened and it possesses at 

 least two spines. Th. I 1 arises from near the 

 apex of the sicula and grows vertically downward 

 parallel to the sicula for practically the whole of its 

 length ; there seem to be indications, however, 

 of an upward direction of growth close to the 

 apertural region. A stiff long spine (from 1*5 — 2 

 mm. in length) is given off from the point where 

 this apparent change in direction of growth takes 

 place. Th. I 2 appears to originate from th. I 1 and 

 to grow upward and outward. It possesses a spine 

 similar in size and position to that of th. I 1 . The growth of the subsequent 

 thecas seems to be entirely upward. 



In the majority of compressed examples 

 only three basal spines are presented — one 

 central (from the sicula) and two lateral (one 

 each from th. I 1 and th. 1~), and it was the 

 presence of these which suggested the specific 

 name. Occasionally, however, specimens are 

 met with which show four or even five 

 basal spines. Whether th. I 1 and th. I 2 each 

 possessed a pair of spines or whether the 

 aperture of the sicula was provided with more 

 than two spines (comp. Ruedemann) is uncer- 

 tain from our British examples. 



The test of the polypary seems to be 

 reduced to a mere film and is possibly punctate. 

 The thecse assume very different appearances 

 (Lapworth, 1880, loc. cit.). In the obverse 

 aspect they may appear quite normal, with the 

 short free edge and everted aperture showing 

 clearly (Fig. 200 j), but if much compressed 

 the free edge seems to be squeezed out into a knob (Fig. 200 d) or occasionally 

 may even be drawn out to appear submucronate (ibid.) ; while in the reverse 



39 





a. Young- example, obverse aspect, show- 



ing- sicula and th. I 1 and th. I 2 with 

 basal spines. On same slab as PI. 

 XXXII, fig. 12 c. 



b. Young example, reverse aspect, on 



same slab as Fig. 200 a. 



c. Proximal end showing two sicular 



spines in addition to those of th. I 1 

 and th. 1-. The Cornice, Hartfell ; 

 Hartfell Shales. Coll. Lapworth. 



Figs. 200 d—j. — Cryptograptustricornis (Carr.). 



$ 





8 



S 



■■', 



h i j 



200 d — j. Specimens in low relief, showing the 

 various appearances presented by the 

 thecoe in different views. Laggan Gill, 

 Girvan ; Ardmillan Series. Figs, d — g on 

 same slab. Coll. Lapworth. 



