Perissocytheridea rugata Swain 1955

Perissocytheridea rugata Swain, 1955

Perissocytheridea rugata Swain, 1955, pp. 622, 623, fig. 33c, pl. 61: figs. 4a–b, pl. 62: figs. 6a–b.

SHAPE.—Female carapace outline in lateral view subovate; greatest height anteromedially at anterior cardinal angle. Dorsal margin of valves nearly straight with strong arching above anterior cardinal angle and small convexity above posterior cardinal angle; ventral margin as seen from interior has small convexity in front of middle and is gently convex throughout remainder. Ventral margin not visible on exterior because of ventral swelling of valve and overhang; both dorsal and ventral margins converging posteriorly. Anterior margin broadly rounded, extended below, subtruncate above, sloping down to short, broad, blunt posteroventral caudal process. Carapace outline in dorsal view subelliptical, inflated; greatest width behind middle at alate extensions. Anterior end broadly rounded, posterior end bluntly rounded.

ORNAMENTATION.—A rather weak anteromedian groove or sulcus extending almost vertically from near dorsal margin beneath cardinal angle down to approximately midheight. Exterior of valves covered with well-developed reticulate pattern. Two rounded, submarginal ridges subparalleling anterior margin; one of them continuing as strong ventral ridge swinging upward and forward just before reaching posterior and forming a low alate structure. Several moderately strong sinuous longitudinal ridges present; upper ridges extending from sulcus to posterior end, lower ridges extending from anterior and below sulcus but terminating before ridges above. Two of the lower ridges terminating on moderately weak posteroventral alate structure or node located about two-thirds of shell length from anterior; alate structure is anteroventral to the weaker, more posterior one. Carapace strong and heavily calcified.

SIZE.—Right valve of adult female; length 0.50 mm, height 0.31 mm. Left valve of adult female: length 0.52 mm; height 0.34 mm.

INNER LAMELLA.—Moderately broad, widest anteriorly, but width not very variable. Inner lamella and line of concrescence slightly separated anteriorly, producing very shallow vestibule; marginal selvage rather strong; distinct list visible midway between inner and outer margins.

MARGINAL PORE CANALS.—Very few, abundant anteriorly (about 6 or 7), fewest in caudal extension (about 3); simple, thin, widely spaced, straight to slightly curved, few false canals present anteriorly.

HINGE.—Antimerodont. Hinge of right valve consisting of raised terminal elements separated by long, rather coarsely crenulate groove; raised anterior dental element consisting of 5 or 6 vertically elongate cusps, raised posterior dental element also subdivided into 5 or 6 elongate teeth which increase in size posteriorly. Hinge of left valve consisting of terminal denticulate sockets separated by long crenulate median bar overlaid by narrow accommodation groove.

NORMAL PORES.—Moderately few, scattered, very large, sieve type.

MUSCLE SCARS.—Pattern consisting of a nearly vertical row of 4 small adductors, a larger ovate antennal scar anterior to and slightly above top adductor, a lower mandibular scar, and several scattered, circular dorsal scars.

EYE SPOTS.—Absent.

SEXUAL DIMORPHISM.—Pronounced. Males not as high with respect to length and more inflated posterodorsally than females; females ventrally more inflated than males (Van den Bold (1963) noted that although it has been widely reported that the male carapaces are shorter and higher than the female and the females are longer with posterodorsal swelling, just the reverse is true.)

MATERIAL.—In bottom samples 293 specimens collected from Redfish Bay, 4 from Laguna Madre, and 341 from Copano Bay.

MATERIAL.—Eight specimens collected in bottom samples from Redfish Bay, 2 from Laguna Madre, and 81 from Copano Bay.