34 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



6Ch 



Fig. 44 Yoldiella lata. Lateral view of a shell from the right side 

 and detail of the hinge-plate of a right valve. Specimens from Sta. 

 316 West European Basin. (Scale = 1.0 mm). 



Fig. 45 Yoldiella lata. Right lateral and dorsal views of shells to 

 show changes in shape with growth. Specimens from Sta. 

 INCAL/DS 06 West European Basin. (Scale = 1.0 mm). 



The shell is similar in shape to Yoldiella jeffreysi but more 

 fragile, more compressed, and has fewer hinge teeth on a 

 narrower hinge plate. With increasing length there is a 

 gradual increase in the posterior umbonal length/total length 

 ratio. There is little change in the height/length or width/ 

 length ratios (Fig. 46). Hydroids are present on several 

 specimens at the antero-ventral shell margin. 



Internal morphology (Fig. 47). With the exception of the 



-W/L 



40 J 

 80n 



60- 

 60n 



40- 



- .-":^i»^r. 



H/L 





• v "vLi fAi. 1 "y 



PL/TL 



JVJT 



n25 



15 No. 



1l_J 



3 

 Length 



Fig. 46 Yoldiella lata. Variation in the ratios of height H/L, width 

 W/L and postero-umbonal length PL/TL to length against length 

 of a sample from Sta. BG V CP 07 from the West European 

 Basin. 



Fig. 47 Yoldiella lata. Lateral view from the right side of the 

 internal morphology of a specimen from Sta. BG III DS 50 West 

 European Basin (Scale = 1.0 mm). For identification of parts see 

 Fig. 34. 



