Subfamilies, Genera, and Subgenera — Recent and Fossil 117 



Respiratory and Renal Systems. Tlie pseu(l(jl)rancli (P) is a somewhat 

 triangular i)ro('ess in lucidum (plate 11, figs. 1, 2) and anatinuni (plate 9, 

 fig. 3) but in ho)J))iani appears to be narrower and more cylindrical (plate 

 10, fig. 3). The rectum is very large and the anus discharges just above the 

 base of the pscudobranch. The pneumostome is very large (PS). 



The kidney of Drepanotrema hoffmani (plate 46, fig. 14) is very long 

 and ribbon-like (15 mm. long). The ureter is very short and curves upward 

 at right angles to the long axis of the kidney. A cross section near the 

 middle (fig. 15) shows the kidney to be much flattened, the lumen wider 

 than high, and the veins flattenecl and elongated in section. The kidney of 

 lucidum is shorter and a section near the middle shows it to be more 

 flattened than hoffmani, the lumen regularly long-ovate and the veins 

 smaller and more 'regular in form (fig. 16). 



Digestive System, The stomach (plate 48, fig. 11) is pyriform, the 

 pyloris tapering to the intestine, which forms a loop over the oesophagus 

 and another loop around the liver as in other genera of the subfamily. The 

 blind sac is two-thirds as long as the stomach. The buccal sac is similar 

 to that organ in Tropicorbis. 



The jaw is horseshoe-shaped and is composed of many small plates 

 arranged somewhat as in Planorbis. About seventy plates were counted 

 on a jaw of lucidum (plate 50, fig. 27) and about as many on a jaw of 

 hoffmani (]ilate 50, fig. 26). 



The radula formula of anatinum. (plate 68, fig. 3) is 18-1-18 with 158 

 rows of teeth. Center tooth squarish with two long, spade-shaped cusps 

 reaching two-thirds of the way to the lower margin of the base of attach- 

 ment. There is a very small cusp on each side of the center cusps high up 

 on the reflection. Lateral teeth (1-6) very wide, with three long cusps, 

 entocone, mesocone, and ectocone. Above the entocone there is a small 

 additional cusp, and above the ectocone there is another small cusp on the 

 first four laterals and two cusps on the 5th and 6th laterals. The inter- 

 mediate teeth (7-10) are very wide with the three main cusps well-de- 

 veloped and with a small cusp above the entocone and a small interstitial 

 cusp between the mesocone and the ectocone. Above the ectocone there are 

 four small cusps on the outer margin of the teeth. The marginal teeth 

 (11-18) are narrower than the intermediate teeth; there is a long entocone 

 and mesocone with a small cusp above the entocone, three cusps between 

 the entocone and mesocone, and five small cusps on the outer margin of 

 the tooth where the ectocone would normallv be. 



In lucidum (plate 68, fig. 2), the formula is 28-1-28 with 240 rows of 

 teeth. The center tooth is like that of anatinum except that the large cusps 

 are longer. The lateral and marginal teeth are similar to those of anatinum 

 except that the cusps are longer. 



In hoffmani (plate 68, fig. 4), the formula is 27-1-27 with 230 rows of 

 teeth. The center tooth is as in lucidum and anatinum. The lateral and 

 marginal teeth are similar to those of the other species figured. 



Dr. H. B. Baker (1930, p. 50) has examined the radula of ahcnum and 

 says 'The radula and jaw of D. ahenum are also much as in D. lucidum. 

 The radula formula is 30-1-30, with 194 transverse rows. The marginal 

 teeth are slightly broader at the tip of the cusped reflection and may 

 develop two interstitials between the entocone and mesocone.' 



