56 NORTH AMERICAN 



IRONUS, Bastian, 1865. 



Fig. 13, Plate V. 



30 



12. Ironus americanus, n.sp. : : 2.3 mm. 



1.6 2.3 2.7 2.9 1.3 



The moderately thin layers of the transparent, colorless, naked cuticle 

 appear to be destitute of striations. There are three somewhat conoid lips, 

 which when open, give to the head a somewhat truncated appearance, when 

 folded a somewhat rounded appearance. Each lip bears internally a slightly 

 arcuate, conical tooth, whose altitude is somewhat greater than the width 

 of its base. When the mouth is so opened that the apices of these refractive 

 teeth are about on a level with the anterior extremity their bases lie a little 

 in front of the bases of the cephalic setae. The apices of these teeth are 

 slightly blunt and they have a slight outward curvature. The walls of the 

 pharynx are strongly refractive, and have about the same thickness as the 

 walls of the cuticle. The chitin of the walls of the pharynx, however, is 

 more refractive than that of the cuticle. In this respect it resembles the 

 chitin of which the teeth are composed. Except for the teeth at the mouth 

 opening the pharynx is unarmed, but presents on the dorsal side about half 

 way between the head and its posterior extremity three or four exceedingly 

 minute projections with corresponding depressions. The oesophagus begins 

 near the base of the pharynx, at least it is at this point that the radial struc- 

 ture becomes pronounced. At first it is about two-thirds as wide as the cor- 

 responding portion of the neck. It enlarges a little and very gradually, so that 

 finally it is about half as wide as the base of the neck. The lining of the 

 oesophagus is an exceedingly distinct feature throughout its length. It gen- 

 erally has the appearance of three refractive lines occupying a space nearly 

 one-fourth as wide as the oesophagus itself. There is a large cylindroid 

 or hemispherical cardia, one-third as wide as the base of the neck. The in- 

 testine, which is separated from the oesophagus by a deep, narrow and dis- 

 tinct constriction, becomes at once about three-fifths as wide as the body. 

 Its cells contain scattered granules of variable size, the largest of which have 

 a diameter nearly equal to the width of the refractive portion of the lining of 

 the oesophagus, and the smallest of which have a diameter not more than 

 one-tenth as great. The body wall is thick, generally occupying about three- 

 fifths of the diameter of the body. The lateral fields are a little more than 

 one-third as wide as the body. Nothing is known concerning the renette 

 or the excretory pore. There is no spinneret. The tail, nevertheless, con- 

 tains small cells near the anus which bear a certain resemblance to the ordi- 

 nary caudal glands. From the slightly elevated vulva, the vagina leads in- 

 ward at right angles to the ventral surface half way across the body where 

 it joins the two symmetrically-placed uteri. The reflexed ovaries reach 

 three-fourths the distance back to the vulva, at least in specimens which do 

 not contain eggs. The ovaries contain about a dozen ova arranged for the 



