640 



ARTHROPODA 



SUB-KINGDOM VII 



is seldom well defined; but, on the other hand, the head is sharply demarcated 

 from the rest of the body, and is usually provided with two pairs of antennae 

 and two large eyes, in addition to which there is often a small unpaired eye. 

 About the mouth are the large upper lip (hypostoma), two broad cornute 

 mandibles without palps, one or two pairs of maxillae, and often a lower lip 

 in the form of two elevations below the mandible. 



To the thorax are attached foliaceous, overlapping, biramous legs ; these 

 usually occur in considerable numbers, and while rarely more than eight pairs, 

 they may vary from four to forty, and become smaller posteriorly. They 

 serve for swimming and grasping, and as a rule are supplied at the base with 

 respiratory tubes. The abdomen is partly without legs and frequently ends 

 in a segment bent down or recurved, and furnished with two claw-shaped or 

 expanded caudal appendages. All Phyllopods have the sexes distinct. The 

 males are usually much less numerous than the females, and the latter produce 

 chiefly by parthenogenesis. 



Order 1. BRANCHIOPODA. Latreille. 



Ten to forty or more pairs of leaf-like feet ; carapace, when present, shield-shaped or 

 bivalved ; in the latter case enclosing the whole body and capable of being closed by a 

 transverse adductor muscle. 



Recent Branchiopods are almost exclusively inhabitants of fresh or brackish water, 

 the exceptions being found in strong brine, as in Great Salt Lake, etc. The males are 

 usually less numerous than the females, and in the case of some species several years 

 may pass without their appearance, the females reproducing parthenogenetically. 



Family 1. Limnadiidae. Baird. 



Carapace bivalved, containing the whole body, and closed by a transverse adductor 

 muscle. Antennae well developed ; eyes sessile ; thoracic legs in ten to twenty-eight pairs, 

 'he first one or two pairs in the male forming clasping organs. Abdomen small, 

 without appendages, and terminated by a pair of caudal processes. 



Estheria, Riippel (Figs. 1332, 1333). Shell composed of two thin rounded valves, 



FIG. 1332. 



l:*th:-ria minuta, Alberti. Lettenkohle Dolo- 

 mite ; Sinsheim, Baden. A, 1/1- B, 6/j. C, 

 Portion of the exterior, so/j. 



1333. 



Estheria, sp. indet. Lower 

 barren Coal Measures; Carrollton, 

 Ohio. Umbonal portion showing 

 muscular or nuclear node, is/i. 



united by a straight toothless margin. External surface concentrically ridged or 

 striated, and between the ridges are more or less regularly interlacing or branching 



