VOL. XII, 



1889. 



PROCEEDINGS OP THE NATIONAL MUSEUM. 283 



Genus MYONERA Dall. 



Myonera paucistriata Dall. 



Plate xin, Fig 12. 

 Myonera paucistriata Dall, Bull. Mas. Comp. Zool., xn, p. 302, 1886. 

 Necera paucistriata Dall, Hush, Trails. Conu. Acad., vu, p. 473, 1885. 



Hab. — Florida Keys and Windward Islands, in 339 to 464 fath- 

 oms, bottom temperature 41°.5 to 45° F. IT. S. Fish Commission Sta- 

 tions 2644, 2678, 2751, and 2754, ranging from Cape Fear, North Caro- 

 lina, to Tobago, in 193 to 880 fathoms, temperatures 27°.9 to 43°.4 F. 



To the description already published of the soft parts of this extremely 

 fragile and delicate form several points can be added from the ex- 

 amination of the fresh specimen. The only correction to the original 

 description relates to the opening of the anal siphon, which is a minute 

 circular orifice in a delicate membranous area which in life probably 

 projects in a dome like manner, but in alcohol appears tense and flat. 

 The opening is into the upper portion of the peripedal chamber, of 

 course, as in the other species. That which I took for the anal opening 

 in the first specimen examined was an accidental lesion, while the true 

 anal opening from its minuteness was overlooked. 



The mouth, as stated in 1886, is a simple opening without palpi. The 

 latter are represented, if at all, by a delicate slightly elevated ring of 

 tissue which surrounds the circular mouth. The absence of gill lamiuai 

 is fully confirmed. The septal orifices on the ventral surface are hardly 

 observable without the closest scrutiny, though easily visible on the 

 dorsal surface of the septum. There are eight, as in the Cuspidaria 

 patagonica, and their lips slightly elevated, usually appear triple, so as 

 to give a triangular aspect to their junction. When sounded by a del- 

 icate probe they appear sub tubular. 



The muscular tissue of the septum is concentrated in two bunches of 

 coarse fiber-bundles, which radiate from the posterior outer corners of 

 the septum, suggesting that the fibers, usually devoted to retracting 

 in a nearly vertical plane the siphons toward their angular insertion 

 (pallial sinus) on the shell, are here spread in a horizontal plane. Beside 

 the fasciole of fibers at the corners, there is a loosely arranged central 

 bundle behind the foot, while the rest of the septum is more thin and 

 fibrous, and the vertical roots of the septal muscles far less strong and 

 prominent in proportion than in Cuspidaria. The arrangement of the 

 fibers of the muscular tissue is singularly loose, and in the central area 

 irregular ; quite different from the solid tissue of the septum in Verti- 

 cordia, or the compact bands observable in Cuspidaria. 



The most noticeable feature in this specimen was the condition of the 

 ovaries. These ramified over the posterior part of the visceral mass, 

 terminating in bifurcated or trifurcated sacs, largest at their distal ex- 

 tremity, and somewhat fig shaped. These were crammed with ova and 

 projected from the surface of the visceral mass into the upper chamber 



