882 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Discussion.—This genus suggests Macrocoelia, Platymena, or Opikina. The 
nature of the pseudopunctae is like that of each of these genera, but exterior and 
interior details will serve to distinguish them. 
Glyptomena differs from Macrocoelia externally in the presence of a well- 
marked foramen, the well-developed pseudodeltidium, and the zonated character 
of the ornamentation. Inside the pedicle valve the muscle field is small and the 
diductors are marked by a single median ridge only ; in the brachial valve Glypto- 
mena has a modest development of the median ridge and scarcely any trace of 
the 5 accessory septa which mark Macrocoelia. 
Platymena is like Glyptomena inside the brachial valve, but the flat brachial 
valve makes an easy mark of distinction. This flatness of the brachial valve leads 
to other internal differences. The visceral region of Platymena is depressed be- 
low the somewhat thickened marginal region. 
Opikina can be readily distinguished from Glyptomena externally because it is 
usually more or less strongly geniculated and its ornamentation is not so beauti- 
fully zoned as that of Glyptomena. These distinctions do not hold in all cases be- 
cause some species of Opikina are not very noticeably geniculated and a few have 
fairly well zoned costellae, particularly in the young stages. In spite of these 
difficulties, the interior of the brachial valve of Opikina, in all known species, 
has the septa strongly developed. In some instances the anterior septa are buried, 
particularly the median one, but the lateral septa and adductor ridges are usually 
well marked. 
GLYPTOMENA ? BELLA Cooper, new species 
Plate 246, A, figures I, 2 
Shell fairly large, attaining a width of over an inch; subrectangular, wider than 
long ; sides gently rounded, subparallel ; hinge equal to or narrower than the mid- 
width; anterior margin broadly rounded; costellae well differentiated but zona- 
tion narrow, 3 or 4 of the fine costellae separating the larger ones. 
Pedicle valve gently and evenly convex in lateral profile; maximum convexity 
near the middle; anterior profile broadly convex, the median region somewhat 
narrowly humped; umbo narrowly convex to form a low fold that extends more 
or less distinctly nearly to the anterior margin; median region gently swollen; 
lateral slopes long and gentle; anterior slope long and gentle. 
Brachial valve moderately concave in lateral profile and with the maximum 
concavity at about the middle; umbo sulcate, the sulcus extended anteriorly 
beyond the middle; sides and anterior margin gently curved toward the brachial 
valve. 
Measurements in mm.— 
Brachial Hinge Thick- 
Length length Midwidth width ness Height 
Fidlotype ho) leh hd aS 18.7 fy 24.8 23.4 ? 2.8 
Paratype (117852b).. ? 21-3 29.1 ? 31.0 ? ? ? 
fe (117852c).. 20.0 ? 25.3 25.2 ? 2.6 
Types.—Holotype: 1178524; figured paratype: 117852b; unfigured paratypes: 
117852c,d. 
