Characters o/Lingula anatina. • 5 



distance from the dorsal valve. The oesophagus, which passes 

 between two muscles that attach themselves to the median 

 shell-plate, is imbedded in the anterior division of the liver. 

 The stomach, also similarly imbedded, is in connexion with 

 the gastro-parietal band. The intestinal canal runs directly 

 backward through the liver and genitalia : arrived at the 

 posterior part of the splanchnoccele, and after making a few 

 flexures, vertical and horizontal, it emerges at the ventral 

 surface of the genitalia : next, running forward alongside the 

 right post-latero-parietal *, it reaches the hind part of the 

 adjacent ante-latero-parietal, penetrating this wall as a vent 



(fig. I,/)- 



Shell-muscles. — There are five pairs, and an odd one. 



Three pairs (j, k, I) are lateral, having their members limited 

 to the sides of the shell. One pair is transmedian (i), each 

 member passing across the middle to reverse sides of the shell. 

 One pair (h) has its members confined to nearly the central 

 region. The odd muscle {g) occupies the umbonal cavity. 



Lateral muscles. — In the dorsal valve one pair (J), which 

 may be termed the anterior, is attached to the median plate, a 

 member passing from each of its sides to the corresponding 

 one in the opposite valve, where the splanchnoccele is widest. 

 The second or outside pair (7) in the ventral valve has each 

 member passing from the outer side of the central muscles to 

 the same side in the dorsal valve, close to the posterior half 

 of the ante-latero-parietal, and in the widest part of the 

 splanchnoccele. The third or middle pair (k) springs from the 

 ventral valve between the central muscles, each member 

 passing to its corresponding side in the opposite valve, in- 

 creasing much in size in the passage, and becoming inserted 

 in front of, and inwardly to, the attachments of the muscles 

 belonging to the last pair. 



Transmedian muscles (i). — In the dorsal valve both members 

 of this pair are implanted in the widest part of the splanchno- 

 ccele, one on the inner side of, and immediately adjacent to, the 

 termination of the laterals h and I. Passing backward, each 

 member crosses diagonally to the reverse side of the ventral 

 valve ; but while one preserves its unity, and terminates by 

 inserting itself near the middle of the left post-latero-parietal, 

 the other is divided in its passage, a division becoming 



* In explanation of the terms right and left side, it is necessaiy to state 

 that in placing either of the valves with its interior upward, and its beak 

 nearest to the observer, the latter part is to be considered the posterior 

 end, and the opposite margin the anterior end : this makes the side 

 corresponding with the right hand the right one, and its opposite the 

 left one. 



