614 



BATRACHIA. 



[XYS- 



Fio. 1177. Venusto- 

 dus robustus. 



robustus, St. John & Worthen. 1875, Geo. 

 Sur. 111., vol. 6, p. 345, Burlington Gr. 

 tenuicristatus, St. John 

 & Worthen , 1875, Geo. 

 Sur. 111., vol. 6, p. 348, 

 Keokuk Gr. 

 variabilis, St. John & 

 Worthen, 1875, Geo. 

 Sur. 111., vol. 6, p. 346, Burlington Gr. 

 venustus, Leidy, 1856, (Chomatodus ve- 

 nustus,) Trans. Am. Phil. Soc. Phil., 

 vol. 11, p. 87, St. Louis Gr. 

 XYSTRACANTHUS, Leidy, 1859, Proc. Acad. 

 Nat. Sci. Phil., p. 3. [Ety. xystra, a 

 tool for scraping ; akantha, spine.] Dis- 

 tinguished from Pbysonemus by the 

 slender, straight outline, and less pre- 

 ponderance of the antero-inferior shoul- 

 der. Type X. arcuatus. 

 acinaciformis, St. John & Worthen, 1875, 

 Geo. Sur. 111., vol. 6, p. 459, Coal Meas. 

 anceps, Newberry & Worthen, 1866, (Dre- 

 panacanthus anceps,) Geo. Sur. 111., vol. 

 2, p. 122, Coal Meas. 

 arcuatus, Leidy, 1859, Proc. Acad. Nat. 



Sci. Phil,, p. 3, Up. Coal Meas. 

 mirabilis, St. John & Worthen, 1875, 

 Geo. Sur. 111., vol. 6, p. 458, Coal Meas. 



XYSTRODCS, Agassiz, MSS., 1859, and St. 

 John 1870, Proc. Am. Phil. Soc., vol. 

 11, p. 436. [Ety. xystra, an instrument 

 for scraping; odous, tooth.] Mandibu- 

 lar posterior teeth triangular; great 

 transverse breadth of the inner margin 

 as compared with the longitudinal di- 

 ameter ; coronal surface plain, de- 

 pressed, and alated posteriorly ; max- 

 illary posterior teeth cuneiform, and 

 narrow transverse diameter at the inner 

 margin. Type X. striatus. 



bellulus, St. John & Worthen, 1883, Geo. 

 Sur. 111., vol. 7, p. 183, Coal Meas. 



imitatus, St. John & Worthen, 1883, 

 Geo. Sur. 111., vol. 7, p. 180, St. 

 Louis Gr. 



inconditus, St. John & Worthen, 1883, 

 Geo. Sur. Ill, vol. 7, p. 179, Keo- 

 kuk Gr. 



occidentalis, St. John, 1870, Palaeontology 

 of Eastern Nebraska, p. 244, syn. for 

 Orthopleurodus carbonarius. 



simplex, St. John & Worthen, 1883, Geo. 

 Sur. 111., vol. 7, p. 178, Upper Burling- 

 ton Gr. 



verus, St. John & Worthen, 1883, Geo. 

 Sur. 111., vol. 7, p. 181, Kaskaskia Gr. 



CLASS BATRACHIA. 



[Ety. batrachoS) frog.] 



THE Batrachia live a double life that is, both on land and in water and are 

 called Amphibia. [Amphi, on both sides, around ; bios, life.] They approach the 

 fishes in their early stages of growth, and resemble the true Reptilia in their more 

 mature development. All possess lungs, but during their young or larval condi- 

 tion they are always furnished with branchiae, and in some orders these remain 

 throughout the life of the animal. They form a distinct transition from aquatic 

 fishes to exclusively air-breathing reptiles. They are all strictly oviparous, although 

 in some species the eggs are retained in or upon the body of the parent until the 

 young have attained some degree of growth. After leaving the egg, the animals 

 undergo a series of transformations before arriving at their complete or perfect state. 

 In their early stage they are known as tadpoles, little, fish-like animals, with broad 

 heads, sack-like body, and long, compressed tail. The mouth is at the lower part 

 of the front of the head, and is furnished with a pair of horny jaws, with which 

 they feed upon the animalculse that furnishes the food. They are vertebrated ani- 

 mals, with cold blood and naked skin, and undergo a metamorphosis or change of 

 condition from an aquatic respiration by gills to an atmospheric respiration by lungs, 

 and a consequent alteration in general structure and mode of life. 



