OETACEA. 69 



from the Antwerp Crag, including examples of the tympanies, and 

 some English Red Crag specimens have been identified as belonging 

 to this species by Mr. Lydekker (Quart. Journ. Geol. Soc, Vol. 

 KLIII., p. 8, 1887). The tymTpa,n\c o( -Balcena p7'imige7iia is said 

 to agree with that of B. hiscayeiuis and B. australis in the con- 

 vexity of the inferior border, in the absence of a produced antero- 

 inferior angle and in the comparative lowness of the Eustachian 

 portion of the aperture. Mr. Lydekker recognises much variation 

 in the forms referred to this species, and that which he regards 

 as typical has " the inner wall very high, its superior border oblique, 

 the flattening of the exterior surface extending nearly or quite 

 down to the border, the involucrum considerably thickened, and 

 the inferior border somewhat angulated." 



In a second variety " the obliquity of the superior border of 

 the inner wall is excessively developed." 



A third variety " is distinguished by its extreme lateral com- 

 pression and the total absence of any thickening of the invo- 

 lucrum." 



And a fourth variety " is characterised by the lowness of the 

 inner wall, the parallelism of its superior border to the long axis 

 of the bone, the slight downward extent of the flattening of the 

 anterior surface, and the absence of any distinct angulation of 

 the inferior border." 



Examples of this species are to be seen in most collections of 

 Red Crag Fossils. 



Balmna primigenia is only known in the Red Crag Nodule-bed 

 of Suffolk and in the Antwerp Crag (Scaldisian). 



BAli.fflNA (BALiENOTOS) INSIGNIS, Y. BENBDBN. 

 Plate VI., Figs. 4a, b. 



The genera Balcenotus and Baloenula of Van Beneden (Bull. 

 Acad. Roy. Belg., Ser. 2, Vol. XXX IV., p. 13, 1872, and Ann. 

 Mus. Roy. Hist. Nat. Belg., Vol. IV., Part 2, p. 71, 1880) are 

 included by Mr. Lydekker (Quart. Journ. Geol. Soc, Vol. XLIIL, 

 p. 11, 1887) in the genus Balcena. 



Balcena insignis tympanic bones are said to be very much like 

 those of the fourth variety of B. primigenia but are " usually 

 " more inflated, thicker inferiorly and with a distinct angulation 

 " of the inferior border." 



The tympanies of B. insignis and B. balcenopsis are so similar 

 that Mr, Lydekker could only make a separation by referring 

 the larger ones to the former species, and the smaller ones to the 

 latter. 



Several tympanic bones in the British Museum from the Nodule- 

 bed of the Red Crag of Suffolk are referred to the present species, 

 which is only known from this horizon and from the Antwerp 

 Crag. 



