REVISION OF RECENT BAIRDIIDAE 39 



Habitat. — One specimen was collected living in a soft clay with 

 oyster fragments at 25 m depth west of the Sambirano River delta in 

 the Baie d'Ampasindava, near Nosy Be, Madagascar. 



SuBFOssiL DISTRIBUTION. — Nosy Be; common and sometimes 

 abundant in shallow-water carbonate sands and sandy muds, particu- 

 larly near reefs. 



Remarks. — The smooth, streamlined carapace with angulate lateral 

 outline belongs to an extremely common morphologic type. The 

 material on hand, though numerous, is not sufficiently distinctive to 

 be diagnosed reliably. 



Paranesidea, new genus 



Etymology. — Greek para, near + Nesidea. 



TYFE-sPECiEs.—Paranesideaj'racticorallicola, new species. 



Diagnosis. — Carapace with broadly arched dorsum and more or 

 less concave anterodorsal and posterodorsal segments, punctate; 

 anterior and posterior margins of right valve spinose, of left valve 

 frilled; muscle-scar pattern with eight or more subcircular scars 

 compactly arranged rosette-fashion. 



Antenna with distal claw smooth, anterodistal seta thin, fused claw 

 serrate; vibratory plate of first thoracic leg with four unfeathered setae 

 segregated proximally, of equal or diminishing lengths; furca with 6 

 setae, setae 5 and 6 very much shorter than others; copulatory organ 

 massive, with strongly chitinized conical or digitiform distal projec- 

 tions, copulatory tube stout and nearly straight. 



Description. — Carapace robust, more or less inequivalved, exterior 

 punctate; left valve subovate in lateral outline with highly arched 

 dorsal margin, may have slightly concave posterodorsal segment, both 

 anterior and posterior ends broadly rounded, ventral margin straight 

 and curving upward anteriorly and posteriorly; right valve with 

 distinctly 3-segmented dorsal margin showing pronounced angles and 

 more or less concave segments near the two ends, especially produced 

 posterior end, ventral margin very slightly indented, anterior end 

 broadly and obliquely rounded, posterior end rather caudate. Anterior 

 and posterior margins of left valve with many small spines, of left 

 valve with very wide but usually ragged striate frills. Hinge elements 

 thick but simple, smooth. Muscle-scar pattern basically consisting of 

 8 scars in 3 horizontal to arcuate rows; individual scars are oblong to 

 subcircular in shape and rows are closely spaced; net effect is a compact 

 oval rosette or frequently a nearly complete circle of 7 scars surround- 

 ing interior 8th scar. Carapace of many species is basically transparent 

 or translucent with an exceedingly complicated pattern of irregular 

 but consistent opaque areas, each species having its own peculiar 

 pattern. 



