PLATE 20. 



Alexaiiilnmieiiiu agassizi. X 25. 



FiS-s. 1, 2, 4, 9 i-urrcspoiul to lines \, D, B, C of fig. 3, pi, 7 (anterior end). 



Fig. 3, 5, 7, S, are along lines F, G, H, K, of fig. 5, pi. 7 (posterior end). Fig. 7, X 20. 



Fig. 0. Cross section of heart al junelion of its two divisions. 



