538 MISS CROSFIELD AND MISS SKEAT ON THE [Aug. 1 896, 



Genus Ogygia, Brongn. 

 Ogyr/ia marginata, sp. nov. (PL XXYI. figs. 13-26.) 



This is a fine large species, attaining a length of at least 5 inches, 

 although most of the specimens obtained were not more than 

 2| inches long. The description is of the ' forme longue,' except 

 when otherwise specified. 



General form. — A true oval, flat, or gently convex ; trilobation 

 distinct. 



Head. — A broad segment of a circle, surrounded by a striated 

 concave border, which is narrower in front, and at the genal angles 

 is produced into long sharp spines. The length of the head as 

 compared with the breadth is about 2 : 5. The glabella is long, 

 narrow, almost parallel-sided, especially in young specimens, marked 

 off from the fixed cheeks by a deep axal furrow all round. In 

 older forms it is distinctly clavate in front and very slightly con- 

 tracted in the middle. The surface is flat except for the frontal lobe, 

 which is gently convex. There are traces of two pairs of glabella- 

 furrows, (i) behind the convex frontal lobe, (ii) opposite the base of 

 the eyes. These are very indistinct, and absent in much-com- 

 pressed specimens. The neck-furrow is incomplete in the middle, 

 and the two side parts of it run backward towards the narrow 

 marginal furrow: thus the occipital ring, — which has a small 

 tubercle in the centre, — is wider than the posterior margin of the 

 fixed cheeks. The corresponding furrows on the fixed cheeks are 

 broad, deep, and quite straight. The fixed cheeks are continuous 

 round the glabella anteriorly ; they widen out considerably at each 

 side of the frontal lobe, and also in the middle of the glabella in 

 front, where they follow the course of the facial suture and form 

 a slight point. This portion of the fixed cheeks is convex and is 

 marked with striations similar to those on the anterior margin, 

 which it partially invades. The free cheeks are broad, gently convex, 

 with a fairly wide concave margin, and are produced at the genal 

 angles into long sharp spines. On their inner side is a groove 

 running parallel to the surface of the eye. The eye is situated 

 about halfway up the glabella ; it is of medium size, lunate, with 

 the lentiferous surface rather narrow. The facial suture cuts the 

 posterior margin about | of the way out, and is intramarginal in 

 front. It seems to run very near the margin, and forms a small 

 angle in the middle. The hypostome in our specimens is incomplete 

 posteriorly, but is clearly triangular in shape, with a broadly arched 

 base ; at the posterior end, where it is narrow, it is traversed by 

 two pairs of deep converging furrows. The duplicature of the 

 margin, as also the hypostome itself, are covered with fine striations. 

 In the middle of the former the ' suture me'diane de jonction ' 

 described by Barrande is distinguishable. 



Thoracc short, rather less than J of the total length, with eight 

 narrow well-defined segments. Axis narrow, about | the whole 

 width (in the ' forme large/ of which we probably have two 

 specimens, the axis is nearly ^ the whole width) convex, nearly 



