Lapworth— Graptolites of Co. Down. 127 



been almost wholly derived from the equivalent black shales of the Moffat 

 series. Several of these have already been figured by myself in the " Cata- 

 logue of the Western Scottish Fossils," issued under the auspices of the British 

 Association (Glasgow, 1876). 



To such species or varieties as are yet undescribed a brief diagnosis is here 

 appended. 



Genus I. Rastrites, Barrande. (Grapt. de Boheme. PL 4.) 



According to Herr Richter, the thecae in this genus are mere orifices in the 

 periderm of the common canal, and the long isolated and perpendicular tubes 

 are simply ornamental or defensive extensions of the test. (1.) The British 

 specimens which have hitherto come under my notice have afforded no support 

 whatever to this opinion. 



Mr. W. Carruthers figures a magnificent example of Monograptus spiralis 

 (Geinitz), (2) of which a well-marked example of Rastrites peregrinus (Barr.) 

 seems to iorm the initial portion, and to be organically connected with it. I 

 have recently examined the specimens from which the figure was taken, and I 

 am inclined to believe that this appearance is owing to the accidental juxta- 

 position of the two forms. 



1. Sp. I. Rastrites peregrinus. Barr, Plate 5, fig. I. 



The typical form of this well-known species is abundant in the dark shales 

 of Coalpit Bay, a locality which has yielded the only specimens known to me 

 in which the virgula is apparent as a distinct structure. (3). Locality— Coalpit 

 Bay. 



2. Var. hybridus. Lapw. Plate 5, fig. 2. 



This variety is possibly identical with the fragmentary form Rastrites fugax 

 of Barrande. (Grapt. de Boheme. PI. 4. ) Locality — Coalpit Bay. 



Genus II. Monograptus, Geinitz. Restricted. (Die Graptolithen, p. 32.) 



3. Sp. 1. Monograptus triangulatas. Hark. PI. 5, fig. 14. Locality — Coal- 



pit Bay and Tullygarvan. 



(1.) Richter. Aus die Thuringe Gebirge, Zeit. der Deutsch Gesellschaft, 1871. 

 (2.) Carruthers. Geological Magazine, 1868. PI. 5, fig. 1. 

 (3.) Geological Magazine, 1876. PI. 10, fig. 1. 



