NUCULA. 
37 
probably belonged to the genus Schizodus (including Protoschizodus) , as it closely 
resembles shells of that genus in appearance. 
Affinities. — In general shape Thetis {?) trigona, F. A. Romer,^ appears very 
similar and nearly allied, but it is rather shorter, and more angulated behind. 
II. Family. — NuouLiDiE, d'Orbigny, 1843. 
1. Genus. — Nucula, LamarcJc, 1801. 
This genus arose in Silurian times, and is well represented in the English 
Devonian. From the present localities, however, I only know a single specimen, 
and that is only allocated in it on account of its external characters. 
1. Nucula Peotei, Miinster. PI. Ill, figs. 3, 3 a. 
? 1840. Nucula Peotei, Munster. Beitr., pt. 3, p. 54, pi. xi, fig. 9. 
1884. — sp., Clarke. Neues Jahrb. f. Min., Beil.-Band iii, p. 376, pi. vi, 
figs. 10, 11. 
Description. — Shell small, convex, elongate, subtrigonal, very inequilateral. 
Umbo very posterior, incurved, rather large, elevated, apparently proximate and 
facing backwards. Superior margin straight, long. Posterior margin nearly 
straight and perpendicular, obliquely truncated below. Inferior margin mode- 
rately convex. Anterior margin short and very convex. Contour of back very 
convex, becoming almost perpendicular over the posterior edge, and gradually 
sloping out almost flatly in front. Surface marked with a few irregularly placed 
impressed growth-lines, and with more regular impressed microscopic inter- 
mediate striae. 
Size. — Length 19 mm., breadth 14 mm., depth of valve 6 mm. 
BemarJes. — In general shape this shell is strongly suggestive of the genus 
Nucula, but its hinge-line is invisible. It seems exactly similar to Nucula 
Protei, Miinster, excepting that Miinster's shell is very much smaller, shows no 
concentric lines, and has a rather sharper postero-inferior corner. I have 
therefore regarded it as belonging to that shell. 
The Nucula described by Clarke from the Iberger Kalk is so like that I think 
it is identical, although its umbo may be rather larger. 
1 1843, F. A. Romer, ' Verst. Ilarzgeb.,' p. 26, pi. vi, fig. 25. 
