44 Description oj Genera mtd Species. 



the base of the spine there is articulated with tlie telson a spinous process which is 

 evidently the keel of an accessory swinimeret. The cordate portion of the telson 

 appears to have had a depressioTi down the centre flanked by two tumid sides. 

 Unfortunately the crack already mentioned traveres it along the mid-line, so that the 

 position of the anal opening is not known. The uropods have a very short basal joint. 

 The external branch shows the enormously developed blade-like portion extending far 

 beyond the tip of the telson, the outer edge showing the articulations for the row of 

 spines, and the portion of the web usually wanting in the corresponding portions of 

 P. parki filled in. The internal branch is only represented by portions of the median 

 strengthening keel, insignificant as compared with the outer Ijranch, and which doubt- 

 less supported a fringed web. 



Remarks. — Only one specimen is known of this handsome form, the portion of 

 which preserved measures nearly 100 mm. (about 4 inches), and when complete the 

 creature was manifestly still larger. Owing to its length and to its body being sUghtly 

 curved at death, as already explained, the anterior part of its body is fossilised sideways, 

 exhibiting the folded massive limbs, but owing to the enormous widely expanded 

 uropods, the tail fan is exposed with the underside upwards, the intermediate segments 

 adjusting themselves to allow of this twist. This is mainly l^rought about in the free 

 trunk segments, as the tail segments seem to be too completely locked by their articular 

 facets and pivots and by the overlapping of the epimera to allow of much lateral play. 

 Unfortunately a cra<^k runs ol)liquely through the specimen from the telson to the 

 region of the middle of the back of the trunk, and along this line some of the test has 

 broken away. 



The present species is distinguished from P. parki ])y the tapering tail and the 

 enormous external branches of the uropods. 



The species is named after the late Mr. Thomas Stock, the finder, who at one time 

 was secretary to the Edinburgh Geological Society. 



Locality. — Wardie shore, Granton, Midlothian. 



Horizon. — Wardie Shales, (Scottish) Calciferous Sandstone Series. 



Collector. — T. Slock. 



Pekimectukus elegans sp. nov. PI. VI., figs. 2-6. 



Specific Characters. — Small elongate forms measuring from .50-70 nun. Integu- 

 ments thin and smooth. Carapace longer than broad and faintly keeled in anterior 

 part of mid-line and behind the cervical fold with the dorso-lateral and lateral keels. 



