MALACOZOA. rROPIOPODA. LAMELLIBKAXCHIATA, J'jy 



parallel to the hinge six-twelfths, height from the iimboto the 

 margin ten-twelfths. 



A single broken valve found among shell sand, from the 

 Bay of Cruden, sent bv Mr. Alexander Mun-ay, in November, 

 1842. 



Pecten fragilis. :>Iont- Test, Brit, Suppl. 62. — Pecten bullatus, 

 Chemnitz, Conch, vii. 342. PI. 68. f. 649, 3.— Lima bullata, Turt. 

 Brit. Biv. 217. PI. 17. f. 4, o. — Lima fragilis. Flem. Brit Anim. 

 388. 



Genus 3. Ckenella. 

 Shell free, subelliptical, convex, equivalve, isomeral, 

 nacreous ; the hinge with a single abrupt fold or tooth 

 in each valve, and a sinus under the umbo ; the ligament 

 external, in a narrow groove parallel to the hinge- 

 margin ; the umbones prominent and contiguous ; the 

 valves radiatingly striate, and concentrically striulate. 



1. Crenella decussdta. Decussated Crenella. 



Shell stiborbicular, more extended in the direction from the 

 umbones, being somewhat elliptical, equivalve, isomeral ; the 

 valves convex, rather thin, pellucid, nacreous, radiatingly 

 striate, and marked with concentric striidjE, as well as some- 

 what regtdarly spaced growth-hnes or ridges, producing a de- 

 cussated appearance ; the umbones prominent, a little curved 

 to one side at the point, contiguous, and central ; the hinge 

 thin, with a sinus and a thick angular fold in each valve, under 

 the umbo, between which and the m^argin is a narrow groove 

 for the ligament ; the inner surface glossy and nacreous, but 

 not presenting perceptible musctilar impressions ; the margin 

 thinner and crenidate, especially toward the hinge. 



Of this very beautiful shell tvro specimens, from which the 

 above description has been taken, were found among shell 

 sand, from the Bay of Cruden, sent by Mr. Alex. Mm-ray, in 

 November, 1 842. One, entire, but only a third of a twelfth 

 of an inch in diameter, found by ]\Iiss Marion Macgilliwray, 

 is nearly qtiite orbicular ; the other, a single valve, found bv 

 my son. Paid Howard, is a tenth of an inch in diameter, 

 and somewhat elongated, or subelliptical. 



The species was discovered in sand near Dunbar, bv Captain 

 Laskey. It was accurately described by Montagu, under the 

 name of Mytilus decussatus, from a single valve. Beina: obvi- 

 ously not a Mytilus, Captain Brown named it Crenella elliptica, 

 U 



