146 T. Davidson — Upper Silurian Brachiopoda. 



in general character is this loop to that of Waldheimia that I have 

 provisionally placed it with that genus. Exteriorly this small 

 species bears so much general resemblance to some forms of 

 Centronella, and in particular to G. Hecate, Billings (Canadian 

 Journal, May, 1861, p. 63), that previously to having been 

 made acquainted with its loop I had placed the new English 

 species in Billings' genus. Centronella is described by Prof. J. 

 Hall (Sixteenth Annual Eeport of the Kegents of the University of 

 New York, p. 45, 1863) as consisting of two delicate riband-like 

 lamellfe, which extend to about half the length of the dorsal valve. 

 " These lamellee at first curve gently outwards, and then approach 

 each other gradually, until at their lower extremities they meet at 

 an acute angle ; then becoming united, they are reflected backwards 

 towards the beak in what appears to be a thin flat vertical plate." 

 Now our small species does not show these characters, for in all the 

 specimens developed by the Eev. N. Glass the extremities of the 

 principal stems do not converge so as to become united at their 

 lower extremities, but are wide apart, and instead of extending to only 

 half the length of the shell, are prolonged to within a short distance 

 of the frontal margin. The loop is not therefore that of Centronella 

 as described by Billings and Hall. The genus Waldheimia had not 

 hitherto been quoted as far down as the Upper Silurian. Terehratula 

 and Centronella had been so, and we now know that species with 

 short and long loops commence to appear in the Upper Silurian 

 period. 



2. Waldheimia ? Glassei, n. sp. PI. V. Fig. 6. 



Shell small, sub-pentagonal, broadest posteriorly, slightly truncated 

 in front. Dorsal valve slightly convex, curving rather abruptly at 

 the lateral margins, with a median longitudinal groove or depression, 

 commencing about half the length of the shell, and extending to the 

 front, beak incurved, truncated by a small foramen, hinge-ridges 

 well defined, surface of valves smooth, marked by concentric lines 

 of growth. Length 3, breadth 3, depth 2 lines. 



Obs. — About fifteen examples of this species were obtained by 

 Mr. Maw from the washings of some seven tons weight of Buildwas 

 Lower Wenlock Shales. All the specimens procured were of about 

 the same dimensions, none exceeding the measurements above given. 

 Only very few of them were in a perfect state of preservation, and 

 none were in a suitable condition for Mr. Glass's operations, 

 consequently all his endeavours to develope its interior characters 

 proved unsuccessful. It is a rather larger shell than Waldheimia ? 

 Mawei, but bearing some resemblance to it in external shape ; this 

 has prompted me to leave it provisionally with that genus. Perhaps 

 it may possess the interior characters of Centronella, and it will be 

 very desirable to procure specimens suited to Mr. Glass's operations. 



3. Atrypa reticularis, Linne sp. 



At p. 9 of this paper I alluded to the interior characters of this 

 abundant species. Having, thanks to Mr. Maw's liberality, been 



