506 C. Lapivorth — On Scottish MonograptidcB. 



is placed at right angles with the axis of the theca. It is a little 

 concave, and its outer angle forms a slight denticle, which is pro- 

 longed in a short and slender spine lying in the same plane as the 

 orifice itself. 



From M. Galaensis this species is effectually separated hj the 

 fonn and size of the polypary, the prolongation of the virgula and 

 the details of the hydrothecse. From the variety next to be de- 

 scribed it differs chiefly in the form of the hydrothecce and in their 

 amount of overlap. 



Locality. — Eare in the Riccarton Beds at EUiotsfield, Shankend, 

 and Eiccarton. 



Var. dubius, Suess. Plate XX. Fig. 10. 



Graptolitlius colonus, Barrande ; Graptolites de Boheme, pi. iv. 



%• ^•. . 



GraptoUthus dubius, Suess ; Bohmische Graptolithen, Taf. ix. 



fig. 5<x,, 5 b. 



Polypary straight and rigid, four or five inches in length, and 

 with a maximum diameter of one-twelfth of an inch. Virgula 

 distally prolonged. Hydrothecee 20 to 25 to the inch, inclined at 

 an angle of from S0° to 40°, in contact for less than one half of their 

 length; short and broad tubes expanding slightly in the direction of 

 the aperture, the margin of which is concave, oblique, and bears a 

 minute spine. 



In the young state the polypary in this variety closely re- 

 sembles that of M. colonus in size and shape. Adult examples 

 are comparatively narrower, and the maximum diameter is attained 

 very slowly. The chief peculiarities of the variety are afforded by 

 the character of the hydrothecse. Each is a stout tube, of which the 

 length is about twice the transverse diameter. In some views there 

 is a fallacious appearance of contraction in the direction of the aper- 

 ture, but all well-preserved specimens show the peculiar expansion 

 in the central portion of the thecse common to many forms of the 

 Jlisingeri group. When flattened obliquely, the edge of the aperture 

 is seen to transgress for a great distance upon the body of the 

 periderm, so that the orifice must have been very broad. There is a 

 blunt denticle, which is sometimes ornamented with a minute spine. 



Prof. Suess' original example seems to have been in a very poor 

 state of preservation. He figures and describes it in an inverted 

 position, believing the distal extension of the virgula to be radicular. 



Locality. — Common in the higher zones of the Eiccarton Beds at 

 Eiccarton and Hindhope. 



EXPLANATION OF PLATE XX. 



Figs. 



1 a — e Monograptus lobiferus, M'Coy, typical form. 1 a. b. distal portion ; 



1 c. d. var. Nic&li, Hark., proximal end; \ e. var. millepedia, M'Coy. 

 Dobbs Linn. 



2 a — b Monograptus BecM, Barrande, 2 a, proximal extremity of the more recent 



form. Meigle Quarry. 2 b. central portion of broad bilateral example, 

 magn. Frenchland Eurn. 



3 a — c MonograptuH Clingani, Can. 3 a. b, adult example. 3 c. young form. 



Dobbs Linn. 



