1716 



THE YOYAGE OF H.M.S. CHALLENGER. 



the capsule, at right and left, and are directed half backwards, half outwards (towards 

 the frontal fissure between the valves, PI. 123, figs. 1, 8 a). 



The phseodium exhibits in all Concharida the same characteristic shape, and 

 represents a dark conglomeration of phseodellse, filling up the anterior or oral half of the 

 shell-cavity. Usually it is bilobed, divided into a dorsal and a ventral lobe or wing, 

 which fills up the corresponding valve of the shell (PI. 123, figs. 8, 9). The phseodium 

 is commonly more voluminous than the capsule, and surrounds its anterior half, more 

 rarely it encloses nearly the entire capsule (PL 124, figs. 6, 10). Its colour is usually 

 olive, sometimes more greenish, at other times more brownish, in some species nearly 

 black. The phseodellse, or the roundish granules which compose the phseodium, exhibit 

 the same shape as in all other PH^ODARIA (compare above, p. 1535). Sometimes 

 peculiar rather oblong nucleated cells are scattered in great numbers between the 

 phseodellae, probably parasites or symbiontes (PI. 123, figs. 7-9, 9a). 



Synopsis of the Genera of Concharida. 



I. Subfamily 



Conehasmida. 

 Lateral edges of the 

 two valves smooth, 

 without teeth. 



II. Subfamily 



Conchopsida. 



Lateral edges of the 

 two valves dentate, 

 with a series of 

 prominent teeth on 

 both sides. The 

 teeth of both valves 

 catch one into an- 

 other. 



Valves without sagittal keel, 

 nearly hemispherical or 

 slightly compressed. 



Valves without sagittal keel, 

 nearly hemispherical or 

 slightly compressed. 



Valves with a sharp sagittal 

 keel, strongly compressed 

 on both sides, boat- 

 shaped. 



Aboral hinge without horns, . 720. Coneharium. 



I 



Aboral hinge with two horns 

 (one on each valve), 



Aboral hinge without horns, . 



Aboral hinge with two horns. 

 No apical horn, 



Aboral hinge with two horns. 

 Apex also with a horn, 



Aboral hinge without horns, . 



Aboral hinge with two horns 

 (one on each valve). 



721. Conchasma. 



722. Concheltium. 



723. Conchidiuiu. 



724. Conchonia. 



725. Conchopsis. 



726. Conchocera*. 



Subfamily 1. CONCHASMIDA, Haeckel. 



Definition. C oncharida with the lateral margins of the two valves smooth, with- 

 out interlocking teeth. 



Genus 720. Concharium, 1 Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. 



Jena, Dec. 12, p. 6. 



Definition. C oncharida with the lateral margins of the valves smooth, without 

 sagittal keel and without horns on the hinge. 



1 Conchariwm = Small mussel ; 



