108 TWELFTH ANNUAL REPORT. 



14. P. personatus, Leydig. 

 B. Shell striped. 



* Posterior margin tootlied. 



12. P. procurvus, Birge. 

 ** only lower angle toothed. 



15. P. unci7Kitus, Baird. 



Sp. 1. Pleuroxiis liastatus, Sais. 



(Plate I. Fig. 16.) 



PIcuroxus Icevis, saes. 

 Pleiiroxushastatus, p. e. muelTjER. 



* Form somewhat oval, dorsal line strongly curved, posterior mar- 

 gin short, with a tootb below; head short, baak very long, straight- 

 ish; shell obscurely reticulate. Post-abdomen very long, narrow, 

 with small teeth; claw with two basal spines. Color corneous. 

 The sculpture consists of faint reticulations. The ephippium forms 

 a truncation of the upper part of the shell. Length 0.50 — 0.55 mm. 

 The male has a shorter beak; the first foot has a weak hook, and 

 the spermatozoa are spherical. 



? Sp. 2. Pleuroxus stramiiieiis, Birge. 



This form is the American representative of the preceediug, if 

 not identical with it. Birge mentions minute strife in the meshes. 

 P. stramineus is said to be lower than P. liastatus, while its beak is 

 shorter. Undoubted specimens of P. denticulatus exhibit the same 

 differences, an increase in the convexity of the shell accompanying 

 an increase in the length of beak. The form of the abdomen ap- 

 pears nearly identical, if we compare P. E. Mueller's plate IV, fig. 

 18, with the outline given by Birge at plate 11, fig. 11. The color 

 in both is deep, especially during the period when the winter egg is 

 forming. The direction of the reticulations is said to differ, but 

 P. E. Mueller's figure does not furnish positive evidence of this. 

 Length C.6 mm. 



Sp. 3. Pleuroxus trigoiiellus, 0. F. Mueller. 



Lynceus trigonellm, o. f. mueller, lievix, lilljeborg, leydig, fric. 

 Pleuroxus trigoiiellus, schoedler, p. e. Mueller, kurz. 

 ? Pleuroxus ornatus, schoedler. 



Dorsal line strongly arched; the beak rather long, straightish; 



pigment fleck smaller than the eye. Shell faintly reticulate, the 



markings consisting of transparent ridges. Post-abdomen widest 



in the middle, attenuated slightly toward the end, ^vhich is truncate; 



•claw large, with one long and one very small basal spine. The anal 



