Vol. 50.] OLENELXES-ZONE OF THE NORTH-WEST HIGHLANDS. 665 



Oeeneelus reticulates, sp. nov. (PI. XXX. figs. 1-6, 8-14; 

 PL XXXI. figs. 1-7.) 



In the collection under review there are numerous remains of an 

 Olenellus of much larger size than 0. Lapworthi, which in many 

 other respects it greatly resembles. The reticulated ornament on 

 its test appears to be much larger in pattern (compared with its 

 size) than in that species, and this difference, which makes it con- 

 spicuously visible to the naked eye, has suggested the specific name 

 which I propose for the new form. In general aspect it much 

 resembles the elongated variety of 0. Lapivorthi. It differs from 

 that chiefly in the head-shield, which is deeper in comparison with 

 its breadth. The glabella is longer in proportion to the size of the 

 head-shield, and the individual lobes are each more elongated, while 

 the angles made by the furrows with the general axis of the body 

 are more acute. The distal ends of the eye-lobes are not so far 

 removed from the edge of the glabella, nor do they extend so far 

 backwards, but end well in front of the fourth furrow, while those 

 of 0. Lapivorthi extend beyond it. The raised margin that bounds 

 the cheeks is not so wide in proportion ; the genal spine is more 

 slender, and is placed a little more anteriorly, and the notch between 

 it and the pleural angle is deeper than in 0. Lapivorthi. 



The arrangement of the details of its body-segments is similar 

 to that of 0. Lapworthi, but the peculiarities of the pleura of the 

 third segment are even more pronounced, the spines being longer 

 relatively, and sometimes more incurved. The spines on the pleura 

 of the sixth and three succeeding segments are longer and more 

 slender. Tubercles have been observed in the mid-line on the 

 occipital ring, on the axes of the first three free segments, and on 

 several of the posterior ones. They have not been observed on all 

 the intermediate segments, but this may be owing to bad preser- 

 vation or faulty observation, as it is probable that they once existed. 



The telson is long and styliform, and tapers rapidly at first and 

 then decreasingly. Its articulation with the last free segment is 

 well shown in the specimen from which PI. XXX. fig. 12 was taken. 

 Projecting from the posterior margin of the axis of the fourteenth 

 free segment, at about 4- of its width from each side, are two smaE 

 protuberances. Corresponding projections proceed forwards from 

 the hinge-line of the telson, and interlock with them on their outside. 

 Beyond them the anterior edge of the telson is continued in nearly 

 the same line with the hinge, so that the anterior angles of the 

 telson appear to be overlapped by the pleura of the last free segment, 

 A ' lock joint ' is thus formed which does not allow of the telson 

 folding downward beyond a certain angle with the plane of the 

 last segment. 



A detached labrum which may have belonged to an individual of 

 this species is shown, nat. size, in PI. XXX. fig. 13. 



There appears to be a considerable range in the configuration ol 

 different individuals of this species. PL XXXI. fig. 3 represents 

 an elongated form which appears to have been even further elon- 

 gated, and in fact distorted after having been embedded in the rock. 



