FROM NORTHWESTERN EUROPE 19 
Genus MONTICLARELLA Wisniewska 
1932 Monticlarella Wisniewska, pp. 55-57. 
1960 Monticlarella Wisniewska; Makridin, p. 248. 
1965b Monticlarella Wisniewska; Ager, p. H604. 
Type spECIES. Rhynchonella czenstochaviensis Roemer, by original designation. 
EMENDED DIAGNOSIS. Small subpentagonal or subtriangular rhynchonellids ; 
radial ornament always includes striae and usually ribs ; small, sharp beak; crura 
arcuifer. 
STRATIGRAPHICAL RANGE. Upper Jurassic—? Lower Cretaceous. 
DeEscrRIPTION. External characters. All the included species are small, sub- 
pentagonal or subtriangular, symmetrical and biconvex. The valves may be of 
equal convexity or the pedicle valve may be the more inflated. The small, pointed, 
suberect to erect beak does not obscure the hypothyridid pedicle opening ; deltidial 
plates, when present, are small and disjunct. A small flattened interarea and 
distinct beak ridges are developed. 
One of the most distinctive features is the ornament which always includes radial 
striae, even though these may be restricted to the troughs between the ribs. Ribs, 
rounded or subrounded, are usually present, although not on the type species : the 
variation in the development of the ribbing is a useful criterion for specific differen- 
tiation. The anterior commissure is either rectimarginate, uniplicate or slightly 
sulcate. 
Internalcharacters. _Noneofthespecimenssectioned was particularly well preserved. 
Pedicle valve. Dental lamellae are present but are usually only weakly developed 
and invariably only attached, if at all, to the extreme posterior of the valve. The 
teeth are strong and usually inserted almost vertically into their sockets. 
Brachial valve. The median septum, if present, is low ; septalial plates are not 
developed. Inner and outer socket ridges are usually well differentiated. 
The crura are of the type distinguished by Wisniewska as arcuifer. She described 
them as having wide bases, being concave toward the middle and turning distally 
toward the ventral valve where they are terminated by “‘a sort of small crural 
plate in the shape of a hammer’. The author would agree with Wisniewska that 
the genus has a distinctive type of crura. The most distinctive feature about them 
as seen in transverse section would seem to be the way in which, from being initially 
flattened in the plane of articulation, by the development of vertical elements at 
their inner ends, they again become flattened but lying at right angles to the plane 
of articulation and slightly to the ventral side of it. 
Species. The following nominal species are attributed to the genus 
M. czenstochaviensis (Roemer) (1870, p. 247, pl. xxii, figs. 12-14) 
M. lineolata (Phillips) (as figured by Jacob and Fallot 1913, pp. 17-18, pl. i, 
figs. Q-14). 
M. rolliert Wisniewska (1931, pp. 59-60, pl. vi, figs. 10-1) 
M. striocincta (Quenstedt) (1852, p. 455, pl. xxxvi, fig. 24) 
M. strioplicata (Quenstedt) (1852, p. 455, pl. xxxvi, fig. 23) 
M. triloboides (Quenstedt) (1852, p. 455, pl. xxxvi, fig. 29) 
