Subfamilies, Genera, and Subgenera — Recent and Fossil 83 



Respiratory and Renal Systems. The pseiidobranch (of havanensis, 

 plate 12. fig. 4 1 is a thin, leaf-shaped, fleshy organ doubled or folded upon 

 itself. The rectum (Rl lies above the pseiidobranch and has a conspicuous 

 crested ridge extending nearly its whole length, ending some distance above 

 the anus. There is a large pneumostome (PS). In riisei (plate 13, fig. 10) 

 the folded nature of the pseiidobranch is better shown as is also the crested 

 ridge. The crest is present in all species examined. Pilsbry's figure of the 

 pseudobranch of pallidus (1934, p. 53. B» shows a simple folded pouch. In 

 his figure C. the pseudobranch is figured as much elongated. This appears 

 to be a pathologic condition. 



The kidney (plate 46, fig. 11, riisei) is rather long (about 2.5 mm.), 

 the ureter sharply reflected. A cross section near the middle (fig. 12) shows 

 the kidney to be rounded with the lumen rounded, the two veins being at 

 the lower corners of the section. There is no ridge on the kidney but there 

 is a distinct vertical ridge in the mantle to the left of the kidney. A cross 

 section of the kidney of havanensis (fig. 13) shows that in this species this 

 organ is much more compressed and much wider than in riisei; the central 

 lumen is irregularly oval with the two veins placed below the lumen at the 

 outer ends of the section. Of pallidus, Pilsbry says 'The kidney is long, 

 band-like, and flat, with no trace of a superposed ridge' (p. 52). 



Digestive System. Stomach region with distinct division into crop, 

 gizzard, and pylons. There is a large blind sac. The intestine makes a 

 backward loop around the liver and extends forward, the rectum ending 

 near the pseudobranch. The digestive organs are alike in all species 

 examined. The buccal sac is pyriform with a large and conspicuous radula 

 sac which protrudes from the posterior end of the buccal sac as a rounded 

 projection. This sac is longer in obstructus than it is in riisei. The salivary 

 glands are cylindrical, longer than the buccal sac. and joined behind, as 

 in other groups of the Planorbinae. 



The jaw of riisei (plate 50, fig. 12) is composed of three pieces, a wide 

 and low superior part, finely striated along the face, and two lateral pieces 

 which assume the form of a question mark. These are enlarged at their 

 junction with the superior jaw and taper to a point at the lower end. The 

 jaw of obstructus is similar to that of riisei (fig. 11). H. B. Baker has 

 described the jaws of pallidus and kiihnianus (1930, pp. 47, 48). The jaws 

 of Tropicorbis are unlike those of the other genera of Planorbinae (ex- 

 cepting Australorbis) and resemble those of the subfamily Helisomatinae. 



The radula formula of havanensis (plate 68, fig. 8) is 19-1-19 or 

 20-1-20 with 109 to 112 rows of teeth. The central tooth has a broad base 

 of attachment and is bicuspid, the cusps spade-shaped and reaching to the 

 lower margin of the base of attachment. Laterals (1-6) squarish with three 

 cusps, the entocone larger than the mesocone and ectocone. The 6th tooth 

 has a small interstitial cusp on the entocone and two very small cusps 

 above the ectocone. The 7th tooth is an intermediate, the entocone broken 

 up into four small cusps and the ectocone with two small cusps on the 

 outer edge above. The 8th to the 16th or 17th teeth are marginals (8, 10, 

 12), the reflections becoming very long and narrow, with an entocone of 

 four or five small cusps, a single spade-shaped mesocone, and four to six 

 or seven small cusps on the outer edge representing the ectocone. The 

 marginal teeth become narrower toward the edge of the membrane. 

 The outer three marginals are vestigial and are without denticula- 

 tions. The central teeth of the different rows vary in width at the upper 



