PANAMIC-PACIFIC PELECYPODA 449 



forming a seat on which the protoplax once rested. The posterior ends of 

 the valves have a short, brown-colored, tongue-shaped siphonoplax to which 

 is joined a longer calcareous tube of irregular form, notched at the end. 

 The anterior side of the valves is sculptured with scabrous riblets, the 

 posterior side with concentrics. Our largest specimen measures 39 mm. in 

 length. 



Range — Panama to Ecuador. Panama: Bucaro. Ecuador: Crucitas. 



Hastasla esmeraldensis, new species Plate 79, figures 5, 5a 



Like H. tubifera but more slender, the posterior half of the valves 

 longer and narrower, the calcareous tube in all of my specimens quite short. 

 The protoplax is long, narrow, paired, joined to the callum by a narrow 

 neck. Mesoplax short, subquadrate with an outer thin flange, and separated 

 from the protoplax by a transverse slit. No metaplax, the margins of the 

 valves closed by an inner chitinous membrane. 



Length 30.1 mm., height 9.4 mm., diameter 8.8 mm. 

 This species is abundant at Esmeraldas, its burrows excavated in a 

 medium-hard Tertiary shale. 



Range — Ecuador. Ecuador: Esmeraldas. 



Hastasia quadra (Sowerby) Plate 80, figures 2, 2a 



Pholas quadra Sowerby, 1834, Proc. Zool. Soc. London, p. 71 Montem Christi, Columbiae 

 Occidentalis.— Sowerby, 1849, Thes. Conch., vol. 2, pt. 10, p. 499, pi. 106, figs. 

 62, 63. 



Pholadidea (Hastasia) quadra Sowerby, Turner, 1955, Johnsonia, vol. 3, No. 34, pp. 

 95, 96, pi. 58. 



Shell small (length of valves and siphonal tube about 25 mm.), thin, 

 fragile, white, subquadrate, the anterior side higher. Valves divided into two 

 sectors by a narrow, slightly indented, umbonal sulcus, the anterior side 

 beaked and sculptured with scabrous concentrics, the posterior side narrower 

 and with smoother concentrics. Callum large, semicircular, connected with 

 the anterior-umbonal reflection which forms a deeply concave or excavated, 

 platelike area along the anterior-dorsal margins. Siphonoplax chitinous, 

 brown in color, with swellings near the base and connected with a longish, 

 calcareous tube. 



A rare and imperfectly understood species. It is recognized by its shape 

 and the concave, platelike area covering the anterior-dorsal margins. 



Range — Panama to Ecuador. Panama: Guanico. Ecuador: Manta; 

 Crucitas. 



Subfamily JOUANNETIOAE 



Valves pholadiform, short, globose and inequivalve. Internal apophyses 

 short or lacking. Anterior gap open in the juvenile stage, closed by a large, 

 coarse callum extended along or over the beaks in the adult. 



Genus JOUANNETIA de Moulins, 1828 

 Type species by monotypy, /. semicaudata des Moulins, Miocene of 

 Europe. 



Shell large or small, short, globose, with a large, open gap in the 

 juvenile stage, closed by a heavy callum in the adult which overlaps the 

 right valve from the left and may be extended narrowly or widely and lobe- 

 like between or over the beaks. The surface of the disk is divided by a nar- 



