294 ORDER SYNONCHIA, ORDER MESONCHIA 



distance about three times as great as the length of the tail; the posterior ones 

 are a little nearer together than the anterior ones. The two hindermost are 

 opposite the anterior halves of the spicula, while the antepenultimate is a little in 

 front of the proximal ends of the spicula. The average distance between the 

 organs is one and one-half to two times as great as their diameter. No special 

 setae or papillae have been seen on the tail either in front of the anus or behind 

 it. The strongly developed spicula taper at both ends. The proximal ends are 

 slightly hooked toward the ventral side of the body, and also slightly enlarged, 

 so that they are distinctly cephalated. The main portion of the framework of 

 each spiculum consists of four refractive elements arranged in two pairs, one 

 dorsal, the other ventral. The slightly curved accessory piece leaves the surface 

 of the spicula somewhat and then recurves so as to touch them again. The ejacu- 

 latory duct is half as wide as the body. 



Habitat: Mud, tide pool, low tide, Portsmouth, N. H., U. S. A. At first sight 

 this species appears to be a Cyatholaimus but examination shows a number of 

 important differences. The pharynx is not striated in the same way as that of 

 Cyatholaimus, nor is there a dorsal onchium. The examination has not revealed 

 the pores frequently to be seen along the borders of the lateral fields in Cyatho- 

 laimus. Most Cyatholaimi have a single testis. This genus also bears a con- 

 siderable resemblance to Halichoanolaimus, but differs in that the numerous, 

 minute pharyngeal denticles of Halichoanolaimus are lacking. Alternating with 

 each pair of the twelve amalgamated lips there are papillae which extend an 

 exceedingly short distance beyond the margin of the lips. Fig. 75, p. 293. 



IX. Order Mesonchia. 



76. Mesonchium poriferum n. sp. The thickish, colorless cuticle has on the 

 females three rows of round cuticular elements on the lateral fields, on the males, 

 two; similar markings arranged irregularly occur on the ventral surface. Setae, 

 half as long as the corresponding part of the body is wide, are found scattered on 

 the neck. None are seen on the body. Rows of pores occur on the lateral fields, 

 one row on each side just outside the longitudinal rows of lateral markings. The 

 diameter of these pores is about equal to the width of two annules; the distances 



%tcph(4)\w(3) pplOl (6+6) * *^^J2*t!Ljfe_, M separating them longi- 

 ^ --.\A__J>- j L2 2 " 2 - 7 -s 2.i /2 - 4 " tudmally are about 



equal to the diameter 

 ' 5 " of the pores. Lips 

 confluent, rounded, thick. Each onchium 

 appears to be the apex of a plate which 

 forms one of the three faces of the pharyn- 

 geal cavity. These plates are thickened at 

 the anterior end of the pharynx. Pharynx 



ward in a direction parallel to the axis of the head. Neck conoid. Oesophagus 

 conoid, with a faint cardiac swelling, hardly to be called a bulb. Near the 

 nerve-ring, the oesophagus is one-half, and finally three-fifths, as wide as the 

 corresponding portion of the neck. The lining of the oesophagus finds optical 

 expression in three parallel, refractive lines. Its musculature is rather coarse. 

 There is a more or less hemispherical cardia, one-fourth as wide as the base of 

 the neck. The intestine becomes at once three-fourths as wide as the body, its 



