24 BEVISION OF AMERICAN MOLES— rnrE. vol.xix. 



elongated. Zygomatic arch slender, ascending posteriorly. Infraorbi- 

 tal foramen large, oblique. Interorbital area inflated. Parietals broad, 

 triangular, with a concave posterior margin; mastoid and occipital 

 borders equal, mastoids inflated. Foramen magnum high and narrow. 

 Tympanic bulla^ complete, rounded, depressed; meatus auditorius 

 externus small. Palate long, modeiately concave, with a prominent 

 transverse posterior margin. 



Mandible with stout horizontal ramus; ascending r.amus very short, 

 and directed backward. Coronoid broad, triangular, and erect; angu- 

 lar process large, oblong, with a rounded margin posteriorly, and con- 

 cave superior margin. Condyles long, cylindrical, transverse. 



TEETH. 



Functional dentition: i, |; c, ^; pm, | ; m, i| ; total, 30. 



First upper incisors large and long, obtusely pointed, somewhat diver- 

 gent, convex in frimt, flat behind. Second and third incisors minute, 

 slender and simple. Canine two-thirds as long as the first incisor, cus- 

 pidate. First premolar less than half the size of the canine, pim])le, 

 unicuspidate. Second and third jiremolars successively larger, unicus- 

 pidate, with a comi^ressed, trenchant posterior margin terminating 

 below in a tubercle. The third with a very small heel (disap])earing with 

 age). Molars W-shaped in transverse section with a large V-shaped, 

 antero-interual heel or cusp; first and second subequal and quadrate. 

 Second molar with four external, two internal, and one basal cusp. 

 First and third molars with three external, two internal, and one basal 

 cusp. 



First lower incisor small, unicuspidate; second large, elongate, canine- 

 like, grooved internally. Premolars increasing in size from the first to 

 the third; the latter as long as and considerably thicker than tlie 

 second incisor. The posterior edges of the premolars rather trenchant. 

 Molars W-shaped in transverse section, each with two external and 

 three internal cusps. First and second molars subequal and largest; 

 third smaller. 



SKELETON. 



The vertebral formula of Scalops is given by Cuvier and by Bell as 

 follows: c, 7; d, 12; 1,7; 8,(5; ca, 10; total 42. I find by examination 

 of skeletons in the National ^Museum collection that the normal formula 

 is c, 7; d, 14; 1, 5; s, G; ca, 11; total, 43. One skeleton, while ]n'eserv- 

 ing the same number of lumbars, has 15 dorsals, making the total num 

 ber of vertebra' 44. There are 7 intervertebral ossicles, arranged as 

 in Seapanus. The sternum consists of G segments and a very large 

 manubrium, which is exactly as long as the combined segments. The 

 first pair of ribs joins the manubrium near the juuction of its third 

 and last fourth. The ribs are broad and flat. The upper surface of 

 the manubrium is dilated and grooved, with incurved raised edges. 



The keel is triangular, deepest in front. 



