and species of Silurian Radiata. 271 



this one of the most distinctly marked species of the genus. 

 Fragments are often beautifully iridescent. 

 Common in the black shale of Lockerby. 



Graptolites millipeda (M'Coy). 



Sp. Char. Length unknown : occurs in short, curved or spirally 

 inrolled fragments ; cell-denticles on the outer side, each broad 

 at the base and abruptly contracted to a small mucro, de- 

 flected or strongly curved backwards, both the upper and lower 

 margins being sigmoidally curved ; the denticles touch each 

 other (when fully preserved) at their bases ; five or six denticles 

 in the space of 2 lines ; width from axis to end of cell-denti- 

 cles slightly more than half a Hue. 



The much closer, shorter and wider cell-denticles with their 

 abruptly recurved points, easily separate this species from the 

 G. convoiutus (His.), the inrolled form of which agrees with it. 

 I only provisionally characterize the species, as there is a possi- 

 bility that if the G. convoiutus be only the top of G. Sedgwickii, 

 this might ultimately form the corresponding portion of the G. 

 lobi/erus, a supposition which at present however is not supported 

 by any evidence, there not being the same amount of resemblance 

 between the two latter as between the two former species, the 

 difference in size and structure of the cells being much greater. 



Not uncommon in the black shale of Lockerby. 



Diphgrapsis rectangularis (M'Coy). 



Sp. Char. Straight, simple, usually from 1 to 1|^ inch long, 1 line 

 wide, gradually tapering to the base, which is a fine simple 

 point ; axis fine capillary ; cells perfectly at right angles to the 

 axis, forming square denticles to the margin, distinctly sepa- 

 rated by rather wide parallel-sided notches reaching two-thirds 

 of the way to the axis, five in the space of 2 lines. 



This species is more distinct and constant in its characters 

 than most of the allied forms ; in general appearance it approaches 

 the D. pristis (His. sp.), but is easily distinguished by the short 

 square cells, set at right angles to the axis, instead of the narrow 

 very oblique ones of that species. The only Graptolite making 

 any approach in the form and direction of the denticles is the 

 hicornis of Hall, which however is distinguished by the strong 

 lunate process to the base, from which it derives its name ; the 

 base of the present species being a simple point as in the D. 

 pristis ; there is also in most of Mrs. Hall's figures a perceptible 

 obliquity in the denticles, which so admirable an artist could not 

 have designed for this species : the bicarinate base (so coramGnly 

 preserved in the D. bicornis) certainly does not appear in ours. 



