Davidson — Earliest British Brachiopoda, 313 



the ventral valve of O. Sngittalis. D. pileolus wae found by Mr. 

 Hicks to occur in the Middle (Sandstone) beds of the ' Menevian 

 group ' at Porth-y-rhaw, Ninewells, and Solva Harbour, St. David's, 

 where it is scarce and usually very imperfectly preserved. One 

 specimen of a minute Discina (PL XVI. Fig. 1^^) appears to have 

 been obtained by Mr. Hicks in one of the yellowish grey beds of the 

 ' Harlech group,' on the road leading from Solva to Whitechurch, 

 St. Davids ; and if it should turn out to be the same as the shell 

 under description, which it appears to resemble, it would be the 

 oldest form of the genus known, and one of the earliest Brachio- 

 poda on record. B. pileolus was also found by Mr. Belt in the ' Mene- 

 vian ' stage at Camlan in North Wales. 



Genus Acrotreta, Kutorga, 1848. 



AcROTRETA ? NiCHOLsoNi, Dav. PL XYI. Figs. 14-16. 

 Shell small, about two lines in length by about the same in 

 breadth, almost circular, rather wider and broadly rounded an- 

 teriorly, nearly straight posteriorly ; dorsal valve very slightly con- 

 vex ; ventral valve conical, apex sub-central and truncated by a 

 minute circular foramen, which is situated at a little more than one- 

 third of the length of the valve. From the centre of the posterior 

 margin a narrow groove or channel extends to the base of the fora- 

 men, while on either side a small flattened triangular space or false 

 area {?) is limited by an indented line. Surface of both valves 

 marked with numerous concentric lines of growth. 



Although the species under description has not, as far as I am 

 aware, been hitherto found in Wales, it will be desirable to introduce 

 it here, as it is new to Great Britain, and another of those minute 

 and curious forms that have been discovered subsequent to the publi- 

 cation of the first portion of my Silurian Monograph. Several 

 examples of this interesting little species were sent to me in Feb., 

 1867, by Dr. H. A. Nicholson, their discoverer, under the designation 

 of Siphonotreta micula, but I soon perceived that they could not be 

 identified with that genus or species, and although 1 am by no means 

 confident as to the propriety of locating it in Acrotreta, this last is 

 the genus to which our Scottish shell seems to bear the closest 

 resemblance. One valve being nearly flat, the other conical, with a 

 minute perforation at its apex, the longitudinal groove or canal and 

 false area, — all being external features peculiar to the Eussian genus. 

 However, as we know nothing of the interior of Acrotreta, and very 

 little of the Scottish shell, the true generic position of this species must 

 be viewed as provisional. A. ? Nicholsoni occurs in black shales in 

 the Upper Llandeilo ? of Dobb's Linn, near Moffat in Dumfriesshire, 

 whilst Siphonotreta micula is found at Hart Fell, or Glenkiln Burn, near 

 Moffat, in distinct beds. Siphonotreta micula is, strictly speaking, a 

 ' Llandeilo flag ' species, but Mr Hicks believes he has found it, or 

 another undeterminable allied form, in the upper portion of the 

 ' Arenig group ' at Whitesand Bay, St. David's. 



Genus Orthis, Dalman, 1827. 



It will not be necessary here to enter into a lengthened account of 



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