372 Mr. T. II. Withers on the 



three pair of lower latera, making sixteen valv(>s: I believe 

 there must have existed some other latera, but probably 

 only a few more ; for tliese valves, especially the carinal 

 pair, are much larger, in |)roportion to tlie scuta and terga, 

 than in any recent Pu/licipes. Probably the lower latera, 

 together with the sub-rostrum, and perhaps a sub-carina, 

 formed only a single lower whorl." 



For some years now I have not been altogether satisfied 

 in my own mind with Darwin's interpretation of these 

 remains, and more especially their reference to the genus 

 PuUicipes, but, in view of Darwin's opinion as to the number 

 of valves forming the capitulum, it was necessary to get 

 proof before raising any discussion, and by the preparation 

 of a number of specimens this has now been obtained. 



In 1910 (p. 499, text-fig. 4) I figured a small incomplete 

 capitulum of F. unguis showing the right side, and this 

 consisted of the carina, scutum, tergum, upper latus, and 

 carinal latus. That specimen not only showed the scutum, 

 unknown to Darwin, but the valves were preserved in their 

 natural position, and it proved the position of the carinal 

 latus. Darwin certainly did recognise this latter valve of 

 P. unguis as a carinal latus, but, curiously enough, the 

 homologous valve in the closely-related species P. glaber 

 (1851, pi. iii. fig. 10/) was regarded by him as a "Latus 

 (probably from near the rostrum)." 



Two specimens carry the evidence a stage further. One 

 (PI. V. fig. 1) in the Geological Department of the British 

 Museum, registered 59802, exhil)ited the inner surface of 

 the valves of the right side of an incomplete capitulum, and, 

 when these were tilled with plaster and the matrix taken 

 away from their upper surface, the valves were seen to be 

 almost in their natural position and to consist of the carina, 

 tergum, carinal latus, and inframedian latus. The second 

 specimen (PI. V. fig. 2) is in the Sedgwick Museum, 

 Cambridge (Wiltshire collection), and exhibits the carina, 

 and on each side the carinal latus, followed by tlie left and 

 right inframedian latus. 



Turning now to other specimens in the Geological Depart- 

 ment of the British Museum, one, registered 44300, shows 

 remains of more than one capitulum. From this specimen 

 were obtained five peduncular plates, of which two are 

 figured (PI. V. figs. 9, 10), There is on the matrix, in 

 addition to a carina, paired terga, and upper latus, a left 

 carinal latus and two other lateral valves attached together 

 (PI. V. fig. 3). Now one of these last two valves is the 

 opposing valve of that which we know from specimen 59802 



