Characters 0/ Lingula anatiua. 7 



the posterior end of the shell ; but the objection seems to be 

 met by the fact that this muscle is to some extent relaxable, 

 as I have had no difficulty in turning aside the beak of either 

 valve. Further, it might with some reason be assumed that 

 the rostral extremity of the non-pedicle- or unattached valve 

 possesses the greatest freedom of lateral motion; but the 

 assumption requires the posterior terminations of the trans- 

 median muscles to be inserted in the corresponding region of 

 the valve : the contrary, however, is the fact. It is highly 

 probable that careful observations on the habits of the animal 

 of Lingula will remove these two objections : but whatever 

 value attaches to them, or to the mode in which it has been 

 attempted to diminish their force as a counter argument, I do 

 not hesitate to regard the valvular movements, just contended 

 for, to be quite in unison with the following facts : — 



The umbonal muscle (g) is in no way fettered by the 

 pedicle, or any other part. The shell is not only edentulous, 

 but its hinge-margins are widely and totally separated from 

 each other. The beaks have their margins persistently apart, 

 even when the umbonal muscle is most rigid. The post- 

 latero-parietals are highly muscular, necessarily permitting an 

 unusual play of motion between the valves at their posterior 

 extremity. The ordinary muscles {h,j, k, /), principally, are 

 limited to the middle third of the valves — not, as in most 

 Palliobranchs, to their posterior half. All these structural 

 peculiarities are reciprocally related, and they are strictly 

 consistent with the office herein ascribed to the transmedian 

 muscles*. 



* It will be seen by a reference to the ' American Journal of Science,' 

 vol. 1. pp. 103, 1870, that 1 am in complete accordance with the observa- 

 tions of Mr. Morse, who has observed living 1 specimens of Lingula 

 pyramidata, Stimpson, with the valves divaricated laterally at both ends, 

 the axis of motion being evidently located near the centre of the shell. 

 The idea with me was hrst suggested by Mr. Morse's observations. 



Since the above was written I have been favoured bj r Mr. Davidson 

 with an English translation of extracts from the " Reisebericht " of 

 Professor C. Semper, published in the ' Zeitschrift fur wissenschaftlicho 

 Zoologie,' vol. xi. 1860, and vol. xiv. 1864. Semper, who had favour- 

 able opportunities while residing at Zamhuanga, in South America, for 

 studying living specimens of languid anatma, I fiud has anticipated the 

 above observations by Morse. In the last of the volumes cited he 

 mentions that it is a the habit of the animal of this species to displace 

 the valves sideways when it is about to open them. This is never done 

 suddenly or by jerks. The valves are at first always several times pushed 

 to one side and back again on each other, at the same time opening 

 gradually till at last they rest opposite to each other and widely apart." 

 Some sketches sent by Dr. Semper to Mr. Davidson show the two valves 

 crossing each other with a slight obliquity, as in Mr. Morse's figures. 

 Neither of these observers, however, enters into any explanation as to how 

 the lateral displacements are effected. 



