STATE GEOLOGIST. 47 



this spine is serrate with sharp teeth and lies somewhat above the 

 middle of the hight of the animal, so that the free posterior mar- 

 gins of the shell fall much short of reaching the greatest hight 

 of the shell. Post-abdomen of the usual form, with the claws 

 armed with two series of spines or bristles, the outer being much 

 the larger; anal teeth curved or angled, dentate; pigment fleck tri- 

 angular or rhomboidal. Length 2.0 mm., 2.5 mm. 



I am not sure that the three following species are more than 

 varieties; the first in particular is very close to the European type. 



Sp. 3.— Simocephalus congener, Birge. 



My own observations of this form made throughout the Missis- 

 sippi valley are not in complete accord with the description of 

 Birge, but it seems improbable that there is any mistake in the 

 identification. The very generally distributed form on which this 

 species rests is subject to marked variations within certain limits. 

 This species differs from S. serrulatus in the following points. 

 The head, although prominent and spiny near the eye, is not an- 

 gled between this prominence and the beak; in fact, it is either 

 straight or simply curved. The pigment fleck is usually rhom- 

 boidal and only occasionally oval, triangular or irregular. In 

 other respects the agreement is rather close; the terminal claws 

 hare two series of spines, one of which is larger (not, as said by 

 Birge, equal); the outer series is not so much larger as in S. rostra- 

 ius, but not nearly as inconspicuous as in S. vetulus. The termi- 

 nal claws are rather evenly curved. This species is frequently col- 

 ored with pink or brown markings. In old females the back is 

 squarely angled above, forming a pocket for the eggs. The size 

 falls short of that of the last species. I have found this species from 

 the gulf of Mexico to Minnesota. 



Sp. 4. — Simocephalus rostratus. (Sp. n.) 



This form is of the size and color of S. americanus, and approaches 

 nearest to Schodler's S. expinosus in general characters. The back 

 is arched above but not abruptly angled; the spine is as in S. amer- 

 icanus but not so low. The free posterior shell margins are some- 

 what shorter than the greatest hight of the shell. The head is 

 produced below the eyes in an angle like a right angle, which is 

 not spiny. The lower margin of the head is excavated to form a 

 right angle, and in front of the smooth antennules forms a very 

 prominent beak, beyond which the antennules reach but a short 



