Belt— New TriloUtes from North Wales. 295 



Dbsceiption of the Fossils. — ^I. Agnostus nodosus, sp. nov. (Plate 



XII., Fig. 3, a long form, h broad ditto, natural size.) 



Sead, rounded in front, straight at sides, sharply rounded at posterior angles. 



Glabella oblong, obtuse, slightly constricted in the middle, entire, supported by a 



small angular lobe on each side at base ; cheeks, covered vdth deep reticulating 



furrows, radiate next the outer edge ; margin narrow. 



Thorax consisting of two nodose joints. Axis strongly trilobate ; central lobe of 



anterior joint with a strong obtuse tubercle. 

 Tail shaped like head ; axis trilobate, nodose ; central lobe two-thirds the length of 

 tail, narrow in front, widening in the middle, then constricted strongly, and widen- 

 ing again towards the end ; furnished with an oblong blunt tubercle one-third its 

 length of its base. Lateral lobes each composed of two rounded triangular joints ; 

 limb covered with reticulating radiations, divided by a groove reaching from end 

 of axis to margin. Margin narrow, probably furnished with short spines, but not 

 sufficiently preserved to show them excepting obscurely in one specimen. 

 Locality : River Mawddach, above junction with Eden and opposite Dolmelynllyn, ia 

 " Lower Lingula Flags." 



II. Agnostus pisiformis, Lin., var. obesus. (Plate XII., Fig. 4, 

 c broad form, d long ditto, a h nat. size, c d magd. two diam.) 



The typical form of this species is so well known, that I only append the characters 

 in which the variety differs. In A. pisiformis, the axis of the tail is separated at its 

 posterior end by one-fourth its length from the margin. In the variety, the axis 

 reaches nearly to the margin, and in most of the specimens seems to touch it. In 

 the typical form it is only a little more than one-third the width of the tail, including 

 the margin ; in the variety it is more than one-half the width, and is turgid and 

 prominent. Lastly, the grooves in the middle of the axis are but faintly impressed 

 in the typical form ; in the variety they are deeply marked. The margin of the tail 

 is badly preserved, but was probably furnished with short spines. 



Locality with the above, in " Lower Lingula Flags." 



III, Olenus gibbosus, Walh. (Plate XII., Fig. 5, a broad form, 

 b long ditto.) 



I have obtained very fine specimens of this well-known Scandinavian species from 

 the Dolgelly district, and I give figures of the two forms, as Angelin,i Barraude,^ and 

 Salter 3 have all figured the species with the ocular ridge commencing from between the 

 two glabella furrows instead of above them, and none of them have shown the strongly 

 marked articular spaces between the joints of the axis, although Swedish specimens 

 in the Museum of the Geological Society show both these points clearly. Burmeister 

 has figured the ocular ridges correctly, but shows the thorax with fourteen joints in- 

 stead of fifteen, and the tail with six joints instead of five. 



It occurs in older rocks than any other of the English species of Olenus, and, taking 

 the body and tail together, has a greater number of axial rings. It shows some 

 resemblance to Conocoryphe in its strongly marked ocular ridges and articular spaces, 

 as well as in its large pygidiura and in the facial sutures turning slightly outwards 

 above the eye ; but its true affinities, as shewn by the pointed, unfacetted pleurae, are 

 decidedly with Olenus. 



The occurrence of this species in England will most likely be of great assistance in 

 correlating our rocks with those of Sweden. 



Locality with the above, in " Lower Lingula Flags." 



IV. — Pholas-borings, Denudation, and Deposition in S.E. Devon. 

 By D. Mackintosh, F.G.S. 



(PLATE XIII.) 



THE structure and marine denudation of the district between 

 Torbay and Babbicombe Bay has been so ably unravelled by 



' Angelin, Pal. Suec. * Barrande, Systeme Silurian, Vol I., PI. 3, Fig. 7. 



s .Salter and Woodward's Chart of Fossil Crustacea, Trilobita, Fi^'. 13. 

 * Burmeister, Organization of Trilobites, Tab. 3, Fig. 9, 



