Perissocytheridea troglodyta (Swain 1955)

Paracytheridea troglodyta Swain, 1955

Paracytheridea troglodyta Swain, 1955, pp. 623–625, figs. 34a, 38, 6a–c, pl. 61: fig. 7, pl. 62: figs. 9a–c, pl. 64: fig. 6.

SHAPE.—Male carapace outline in lateral view elongate-subrectangular; greatest height considerably in front of middle at anterior cardinal angle. Dorsal margin long, nearly straight; large portion of dorsal margin not visible when viewed from outside because of posterodorsal inflation of valve. Ventral margin, when viewed from inside, slightly sinuate in front of middle and very gently convex throughout remainder; from exterior, midventral portion obscured by ventral ridge. Anterior margin broadly and nearly uniformly rounded, truncate above, extended below. Posterior margin subtruncate above, sloping rather gently down to short bluntly rounded posteroventral caudate process. Carapace outline oblong in dorsal view; valves moderately compressed with greatest width behind middle but little variation in width throughout carapace length. Posterior end blunt and slightly wider than rounded anterior end.

ORNAMENTATION.—Entire valve surfaces strongly ornamented with ridges, pits, and nodes. Short weak depression extends anteroventrally slightly behind and below anterior cardinal angle; a short distance posterior to this groove a longer, well-developed sulcus extends nearly vertically to slightly below midheight. Low, rounded node or tubercle present immediately in front of this strong sulcus and slightly above midheight. Posterodorsal portion of valve behind sulcus inflated and bearing four or five strong, slightly arched and sinuate ridges joined by short crossbars; several of the ridges curve down and subparallel the posterior margin. Several strong central ridges present, uppermost terminating on low node or alate process located behind middle and slightly below midheight. Valve surface indented or depressed between node and prominent ridges at posteroventral corner. Remainder of valve surface covered with large depressions (the largest depressions occur posteroventrally) resulting in subreticulate pattern. Two broad, rounded marginal ridges subparallel the anterior margin. High rim present around periphery of valves. Valves moderately calcified and strong.

SIZE.—Right valve of adult male: length 0.46 mm; height 0.24 mm. Left valve of adult male: length 0.47 mm; height 0.25 mm.

INNER LAMELLA.—Moderately and relatively uniform in width throughout; greatest width anteriorly. Line of concrescence and inner margin coincide throughout; selvage weak and marginal anteriorly but becoming strong and submarginal ventrally and posteroventrally; selvage considerably removed from margin of caudal extension at posteroventral corner; strong list present in both valves about midway between inner and outer margins.

MARGINAL PORE CANALS.—Few, about 8 along anterior, 9 along venter, and 3 along posterior; moderately long, straight to slightly curved, narrow, simple, a few false canals present anteriorly.

HINGE.—Antimerodont; hinge of right valve consisting of anterior short, raised, trilobed dental element; long median, crenulate groove with finer crenulations posteriorly; and posterior high, wedge-shaped, elongate dental element bearing 5 to 6 small denticles. Hinge of left valve consisting of anterior trilobed socket; long median, crenulate bar with first 3 or 4 crenulations larger than others, which decrease in size posteriorly; and posterior, denticulate socket.

NORMAL PORES.—Moderate in number, scattered, rather large, sieve type.

MUSCLE SCARS.—Consisting of slightly curved row of four small, circular adductors; large, clear, circular fulcral point slightly above and anterior to top adductor; large nearly circular antennal scar anterior to fulcral point; and single, elongate, anteroventral mandibular scar.

OVERLAP.—Left valve larger than right and overlapping; greatest overlap anteriorly and ventrally.

SEXUAL DIMORPHISM.—Pronounced; female carapace shorter and higher than male; posterodorsal inflation of female valves not as great as that of males and posteroventral alation appearing somewhat stronger in females than in males. Other features very similar.

MATERIAL.—In bottom samples 107 specimens collected from Copano Bay.

MATERIAL.—Eighteen specimens collected in bottom samples from Redfish Bay and 8 from Copano Bay.