NUCULA. 17 



?Nonl852. Nucula pectinata, R. Kner. Denkschr. d. k. Akad. Wissensch. Math.- 



nat, CI., vol. iii, p. 312. 



— 1885. — F. Notling. Die Fauna der baltiscli. Cenomauge- 



schiebe (Palaeont. Abhandl., vol. ii, 

 pt. 4), p. 27, pi. iv, fig. 12. 



— 1889. — A. Fritsch. Stud, ira Geb. der bohm. Kreideformat. 



iii. Die Teplitzer Schichten, p. 78. 



— 1S93. — — Ibid. v. Priesener Schichten, p. 91. 



— 1897. — — A. Hennig. Revis. at' Lamellibr. i Nilsson's ' Petrif. 



Suecana,' p. 58, pi. iii, fig. 30. 



Description. — Shell thick, triangular or somewhat rhoraboidal ; convex, slightly 

 compressed anteriorly; antero-dorsal border long, slightly convex; postero-dorsal 

 much shorter and concave ; ventral margin curved, the arc of the curve often 

 increasing towards the anterior extremity. Posterior extremity angular; anterior 

 rounded or slightly angular. Umbones prominent, curved inwards and posteriorly ; 

 usually placed rather near the posterior end of the shell. Lunule deeply depressed, 

 broad, cordate, flattened, smooth except for growth-Hues ; escutcheon loug, nearly 

 smooth except for growth-lines. Surface ornamented with numerous (usually 

 50 to 52) radiating and rounded ribs, separated by narrower grooves ; the 

 grooves, and sometimes also the ribs (especially on the earlier portion of the 

 shell), are crossed by numerous growth-lines. There are often also a few distant 

 concentric depressions. A small rib is placed in the grooves of some of the larger 

 specimens. Teeth : anterior about 22, posterior about 9. Adductor impressions 

 deep, near the margins ; the anterior a little larger than the posterior. Margins 

 of valves rather coarsely crenulated. 



Measurements : 



Length .... 



(i) 

 . 29 



(2) 



. 27 



(3) 



. 26-5 



(4) 



. 20 



(5) 



. 17 mm 



Postero-dorsal margin 



. 12-5 



. 13 



. 12 



. 9 



7-5 „ 



Antero-dorsal margin 



. 22 



. 23 . 



19 



, 14 . 



13 „ 



Height .... 



. 18 



. 19 



. 17-5 



. 15 . 



11 „ 



Thickness 



. — 



. — , 



, 15 



, 11 . 



8-5 „ 



Affinities. — This species is distinguished from N. tenera, Muller, 1 and N. pul- 

 villus, Muller, 2 of the Aachen Greensand by its coarser ornamentation, its greater 

 length, broader lunule, &c. From N. arduennensis, d'Orbigny, it is said to differ 

 in the deep lunule and the strong ribs. 



Remarks. — The specimens from the Pliinerkalk of Hundorf, &c, and the 

 Planermergel of Luschitz, &c, which are referred to this species by Reuss, are 

 relatively shorter, and the umbones more acute ; the examples figured by that 



1 J. Muller, 'Mon. der Petrefact. der Aachen Kreidef.,' pt. i (1847), p. 17, pi. ii, fig. 1. E. 

 Holzapfel, " Moll, der Aachen Kreide " (' Palseontographica,' xxxv, 1SS9), p. 200, pi. xxi, figs. 9 — 12. 



2 Muller, ibid., Supplement (1859), p. 11, pi. vii, fig. 11. Holzapfel, ibid., p. 201, pi. xxi, figs. 7, 8. 



3 



