Subfamilies, Genera, and Subgenera — Recent and Fossil 181 



that of exacuous, but the ureter bends backward at a sharper angle and is 

 directed upward into the mantle cavity. 



Digestive System. The stomach is elongated with the gizzard longer 

 than wide and with a rounded pyloris (plate 48, figs. 4, 5). There is a long 

 blind sac or caecum (BS). The intestine (IN) makes a tight loop around 

 the stomach, extends backward to the liver and then makes another loop 

 and runs forward to the rectum. The buccal sac is elongated, with a 

 rounded radular sac. The salivary glands are narrow, looped, and as long 

 as the buccal sac. 



The superior jaw is arched, wide, and low, with the face vertically 

 striated, as in other members of the group (plate 50, fig. 8, exacuous). In 

 umbilicatellus (plate 50, fig. 15), there is a sharp median projection on 

 the lower edge of the superior jaw. In exacuous, there is only a rounded 

 bulge at this point. The side jaws are as in other species of the subfamily. 



The radula of exacuous has a squarish center tooth with expanded lower 

 margins, the two wide, spade-shaped cusps not reaching the lower border 

 of the base of attachment. The lateral teeth (1-6) are squarish, tricuspid, 

 the mesocone longer and larger than the entocone and ectocone. All cusps 

 are sharply pointed. The sixth lateral has a small cusp above the ectocone. 

 Intermediate teeth begin on the seventh tooth, the entocone splitting into 

 two long, sharp cusps and one or two small cusps appearing on the outer 

 margin of the tooth above the ectocone (9-10). ^Marginal teeth (11-15) 

 long and narrow, the entocone splitting into three to four small cusps and 

 the outer margin of the teeth having two to three small cusps above the 

 ectocone. The outer marginals are almost vestigial. The radula of umbili- 

 catellus (fig. 2) is similar in form to that of exacuous. 



The radula data for Promenetus are as follows, two to four specimens 

 of each having been examined: 



Locality Rows Collector 



Winnebago Lake, Wisconsin 110-112 F. C. Baker 



Wainwright Park, Alberta 115 Dr. Swales 



Wainwright Park, Alberta 138-140 Dr. Swales 



Vermilion Lake, Minnesota 140 F. C. Baker 



The material examined for the anatomical data described and figured 

 in the preceding pages is listed below. Figures in parenthesis indicate 

 number of specimens studied. 



cracuou-^: Winnebago Lake, Wisconsin, collected by F. C. Baker (4) ; Lake 

 Nipissing, Ontario, received from the Canadian National Museum (5) ; Mott Lake, 

 Wainwright Park, Alberta, collected by Dr. Swales (4) ; 



exacuous megas: Paul Lake, British Columbia, collected by Prof. D. S. Raw- 

 son (2). 



umbilicateUus: Mott Lake. Wainwright Park, Alberta, collected by Dr. Swales (8) ; 

 North Star Lake, Minnesota, collected by F. C. Baker (1); Vermilion Lake, Minne- 

 sota, collected by F. C. Baker (2) . 



Specimens of exacuous from Wainwright Park, Alberta, were heavily 

 infested with cercariae, more abundant in the ovotestis and liver. In several 

 specimens both of these organs were almost obliterated. 



Geographical Distribution. The genus Promenetus has a wide distri- 

 bution. It has been recorded from ]Maine west to Washington and Oregon 

 and from Hudson Bay and Alaska south to New JMexico and Alabama. 

 A single species {i7nus) is known from Bermuda. 



