. Bulletin. Natural history; Natural history. 36 NATt'RAr, History Survey Vol. 28, Art. 1. Fig. 26.—An adult Ambystoma texanum from Calhoun County, Illinois. The groundcolor is dark brown or black, usually with flecks of gray scattered over the back and sides of the animal. Trends in ontogenetic variation are ex- pressed chiefly by proportions and color and are illustrated by a sample of 22 specimens from Horseshoe Lake, Alexander County, table 5. Geographic variation within Illinois is rather slight. A sample (14 specimens) from the southern tip of the state tends to hav
. Bulletin. Natural history; Natural history. 36 NATt'RAr, History Survey Vol. 28, Art. 1. Fig. 26.—An adult Ambystoma texanum from Calhoun County, Illinois. The groundcolor is dark brown or black, usually with flecks of gray scattered over the back and sides of the animal. Trends in ontogenetic variation are ex- pressed chiefly by proportions and color and are illustrated by a sample of 22 specimens from Horseshoe Lake, Alexander County, table 5. Geographic variation within Illinois is rather slight. A sample (14 specimens) from the southern tip of the state tends to have smaller individuals, slightly lower tooth counts, and perhaps a higher fre- quency of subadults with distinct gray frost- ing on the dorsum than samples from else- where in the state. In 32 per cent of the 14 southern Illinois specimens a single row of premaxillary teeth is characteristic, whereas in only 6 per cent of 37 specimens from other parts of Illinois is a single row characteristic; 2 or 3 rows are typical. Individual variation for a sample of 51 adults is as follows: snout-vent length 50 to 90 mm.; total length 89 to 155 mm.; number of costal grooves 13 to 15 (average ) ; number of vomerine teeth 18 to 33 (average ) ; number of maxillary-pre- maxillary teeth 58 to 101 (average ). A specimen from McLean County has a bifid tail, an anomaly due to an injury to the tail of the animal. Habits.—The small-mouthed salamander is the most common Ambystoma in the state. It occurs in woodlands, prairie, pastured areas, and even in the intensively cultivated black soils of central Illinois. Adults are en- countered during the summer months in various habitats, such as rocky hillsides, creek beds, and floodplain swamps. They feed on earthworms, slugs, and arthropods. They are nocturnal and fossorial. Table 5.—Ontogenetic variation in Illinois Ambystoma texanum. Figures in parentheses are numbers of specimens. Characteristic Snout-vent length as percentage of tot
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