308 Davidson — Earliest British Brachiopoda, 



its length, but, in other respects, does closely approach in external 

 shape to the shell last described. Thanks to the kindness of Mr. 

 Homfray, I have been able to examine a very interesting series of 

 specimens of this species which he had obtained from the * Lower 

 Tremadoc ' at Penmorfa Church, near Portmadoc, in North Wales. 

 It is, however, much to be regretted that the shell rarely presents its 

 true or normal condition, having been much distorted during the 

 process of fossilization. 



Genus Lingula, Bruguiere, 1789. 



Well-authenticated species of Lingula do not appear to have been 

 discovered lower down than the 'Middle Lingula flags,' where the 

 genus would be first represented by L. squamosa — it is true, a badly- 

 made-out species — while L. pygmea, another uncertain species, was 

 found in the * Upper Lingula flags.' In the ' Arenig or Skiddaw 

 Group ' we have L. petalon, but it is chiefly in the ' Llandeilo flags ' 

 that the genus begins to be represented by such shells as L. attenuata, 

 L. brevis, L. granulata, L. Bamsayi, and one or two others. 



Lingula petalon, Hicks, M.S. PL XV. Fig. 16. 



Shell small, broadest about the middle, from whence it becomes 

 rapidly obtusely rounded ; valves much flattened and marked by con- 

 centric lines of growth ; length 5, width 4J lines. 



This shell was found for the first time in 1864, by Mr. Hicks, in 

 the Upper and Lower Arenig or Skiddaw group, at Whitesand Bay, 

 near St. David's ; also, subsequently, in the same formation in Eamsay 

 Island, and Tremanhire, but in no other group. It much approaches 

 in shape to some forms of L. attenuata, but this last-named shell is 

 usually larger and more elongated. 



Genus Obolella, Billings. 



In 1861 Mr. Billings proposed the genus Obolella with the follow- 

 ing diagnosis : " Shell oval, circular or sub-quadrate, convex, or 

 plano-convex. Ventral valve with a false area, which is sometimes 

 minute, and usually grooved for the passage of the peduncle. Dorsal 

 valve either with or without an area. Muscular impressions in the 

 ventral valve, four : one pair in front of the beak, near the middle or 

 in the upper half of the shell, the other pair situated one on each 

 side near the cardinal edge. Shell calcareous, surface concentrically 

 striated, sometimes with thin expanded lamellose ridges. In general 

 form these shells somewhat resemble Obolus, but the arrangement of 

 the muscular impressions is different. In Obolus, the two central 

 scars have their smaller extremities directed downwards, and con- 

 verging towards each other ; but in this genus the arrangement is 

 exactly the reverse." Such is Mr. Billings's diagnosis, but I fear it 

 will require some little modification in its details, if it is to comprise 

 0. chromatica (the tj^pe), 0. ? politay 0. desiderata, O. Sagittalis, 0. 

 maculata, O. ? Salteri, and several other species. Unfortunately the 

 American material in my possession is not sufficiently complete to 

 enable me to determine the point in question ; the interior of one 



