23 



M. 3511. Cast of an immature imperfect right tympanic, not 

 improbably belonging to this variety. The original, which 

 is from Woodbridge, is preserved in the Museum of Prac- 

 tical Geology ; it differs from the tympanic of B. insignis 

 by its narrower inferior surface, more convex anterior 

 border, and its slighter degree of inflation, in all of which 

 respects it resembles No. M. 3509. 



Made in the Museum. 1886. 



The originals of tJie following series of casts (purcJiased, 1883) were 

 obtained from the Antwerp Cray, and are referred to this species 

 by Van Beneden in the 'Ann. Mus. R. Hist. Nat. Belg? vol. iv. 

 pt. 2, to which memoir the following references apply ; all the 

 specimens are preserved in the Brussels Museum. 



M. 1247. Cast of a part of the mandibular ramus ; pi. xix. 



M. 1250. Cast of the left periotic ; pi. xix. figs. 13, 14. 



M. 1251. Cast of the atlas vertebra; pi. xxi. fig. 8. 



M. 1252. Cast of the left ulna; pi. xxi. fig. 7. 



M. 1253. Cast of the left radius ; pi. xxi. figs. 5, 6. 



M. 1254. Cast of a rib ; pi. xviii. fig. 6. 



M. 1255. Cast of a rib ; pi. xviii. fig. 7. 



Balsena balsenopsis (Van Beneden '). 

 Syn. Balfcnula balcenopsis, Van Beneden 2 . 



This is a small species, approaching B. mysticelus in cranial and 

 tympanic structure, its total length being estimated at about 20 feet. 

 The atlas and seventh cervical vertebras are separate, and the other 

 cervicals are only anchylosed by portions of their centra. Van 

 Beneden gives certain characters by which the tympanics can be 

 distinguished from those of B. insignis ; but the writer was unable 

 to recognize these characters in the specimens in the Brussels 

 Museum, and has accordingly referred to the present species only 

 the smaller specimens. 



Hub. Europe (Belgium and England). 



1 Bull. Ac. E. Belg. ser. 2, vol. xxxiv. p. 11 (\$l-2).Balcenula,. 



2 Loc. cit. 



