160 Mr. C. Lapworth on new British Graptolites. 



excavation opposite the thecal aperture ; but it is hardly to be 

 detected under the microscope. The apertural margin wants 

 the concavity invariably seen in the Dichograptidse, and is 

 either straight or somewhat convex. 



Horizon and Locality. Upper Skiddaw slates of Ellergill, 

 Cumberland. 



Family DicranograptidsB. 



15. Dicellograptus complanatus, sp. nov. 

 (PI. V. figs. 17 a-Yl c.) 



Branches of polypary usually straight, diverging from each 

 other at a wide angle ; proximal portion short and straight, 

 with a well-marked radicle and a rudimentary axillary spine. 

 Hydrothecas twenty to the inch, about as long as the width of 

 the polypary, of equal diameter throughout ; apertures per- 

 pendicular to the axis of the theca, slightly concave, opening 

 within a shallow well-marked excavation. 



The branches of the polypary have a width of about one 

 fortieth of an inch at their origin, and gradually augment 

 their diameter till a breadth of one twentieth of an inch is 

 attained. They are of great length and generally straight. 

 Occasionally, however, they bend slightly outwards through- 

 out the whole of their extent. 



The axillary portion of the polypary is formed by the sicula 

 and the two primary hydrotheca3. It is about one twelfth of 

 an inch in extent, and a little rounded proximally. A well- 

 marked radicle is invariably present, but no distinct lateral 

 spines ; and the axillary prolongation of the sicula is short 

 and blunt, and not always visible. 



The branches diverge from the axil at an angle of from 90° 

 to 120°. 



The hydrothecje are precisely similar to those in the genus 

 Climacograptus (Hall). They are short rounded tubes, with- 

 out overlap, placed parallel with the axis of the polypary. 

 No portion of the length of the theca is isolated ; nor is there 

 any distinct appearance of the distal introversion so character- 

 istic of Dicellograptus elegans (Carr.) and its allies. The aper- 

 ture opens interior to the ventral margin of the branch, perpen- 

 dicular to its general direction, within a small excavation 

 in the base of the succeeding hydrotheca. 



The nearest ally of the present species is Dicellograptus 

 Forchhammeri, Geinitz, which differs from it in the character- 

 istics of its axillary portion, and in the striking introversion of 

 the distal extremity of the theca. 



