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71. — Notes on the Fossil Ostracoda. 



By C. Davies Sherborn, F.G.S. 



(Read November 14th, 1888.) 



To the working microscopisfc the common Cypns of our ponds 

 and ditches is a well-known object, and it is the ancestors and 

 relations of Cypris, in the past geological times, that I propose 

 to bring to your notice to-night. 



The literature of the subject is very extensive, the principal 

 contributors being Rupert Jones, Kirkby, and G. S. Brady in 

 England, Reuss, Bosquet, Terquem, Schmidt, Glaus, and Sars in 

 Europe. 



The Ostracoda form one of the lowest groups of the great 

 class Crustacea, and are mostly under 2 mm. in length.* An 

 ostracod may be defined as a crustacean, having the body 

 enclosed in a bivalved shell or carapace, of which the valves may 

 or may not be furnished with hinge-teeth, and are united along 

 the dorsal line by an elastic ligament. 



It is desirable, when studying any group of animals, to classify 

 them according to the structure of the softer parts primarily, 

 and it will therefore be advisable to consider first the structure 

 of one of the most familiar forms, the common Cypris, 



In the genus Cypris the animal is contained entirely within 

 the bivalved shell. The mouth leads, through a narrow 

 oesophagus, to a small " crop," and from thence to a stomach and 

 short intestine. There are seven pairs of appendages. Two pairs 

 of antennae are present ; the second of these in Cypris and Cythere 

 end with strong curved bristles, by means of which the animal 

 can drag itself up or along and fix itself as with an anchor. In 

 the exclusively marine forms this second pair of antennae serves 

 also for swimming. To the second pair of maxillae is attached 

 a fan-like organ, by which the animal produces the necessary 

 circulation of water for respiratory purposes. Near the posterior 

 end of the body is seen the creeping-foot with its strong terminal 

 booklet, and above and behind it the so-called cleaning-foot, 

 furca. The Ostracoda possess single and paired eyes, an 

 auditory organ, and, in the genera Cypridina and Halocypris, 

 another sense-organ situated in front of the single eye. The 

 liver is in the form of two long sacs, one on each side, and over 

 these, in the female, are seen the ovaries. A heart is present in 

 the dorsal region, of Cypridina and Halocypris, but absent in 

 Cypris, Cythere, and others. The nervous system consists of a 

 chain of double ganglia in the abdominal region. The whole 

 surface of the body serves for respiration, an unbroken stream 



* Leperditia Balthica, of ■which some specimens were exhibited by Dr. G, 

 J. Hitide, F.G.S., reaches 15 mm. 



