Invertebrate Gallery of the Indian Museum. 67 



light that exists ; but when they live at great depths to 

 which no sunlight penetrates, their eyes, being then of 

 little or no use, often become atrophied. 



The fresh-water Lobsters, or Crayfish do not occur in 

 India, and all the exhibited specimens of these two families 

 come from Europe and Australia. 



4th Tribe, Penaeidea, Case 39.— This tribe includes the 

 Prawns and contains, two families, the Sergestida; and 

 the Penaeidse. 



In the Sergestidge the fourth and fifth pairs of thoracic 

 legs are rudimentary or absent. Sergestes is the only 

 genus of the family represented in the Gallery, the speci- 

 mens having been taken at great depths in the open part 

 of the Bay of Bengal. 



The Penaeldse foriji a very large family, the members 

 of which have the abdomen very long and well adapted 

 for swimming : very commonly the first three pairs of 

 thoracic legs end in pincers. The female does not carry 

 her eggs about with her when laid. Many Penxidse are 

 gregarious, living in swarms at the bottom of the sea : such 

 is the case with Penxus, Solenocera, and Aristxiis. The 

 Penxidx are very well represented by numerous specimens 

 of the following genera, all from the Indian Seas — Stenopus, 

 Penseus^ Crotalocaris, Aristseus^ Aristasopsis Gennadas 

 Hemipenxus^ Hymenopenanis, Metapenseus, Haliporus 

 and Solenocera. Some species of the deep-sea genus 

 Aristccus are brilliantly luminous. 



5th Tribe, Carldea, Cases 37 and 38. — This great tribe in- 

 cludes the Shrimps and " fresh-water Prawns," and con- 

 tains a very great variety of forms, which have been 

 arranged in a great number of families. 



In the Caridea there are never more than two pairs of 

 pincer-like thoracic legs, and the eggs when laid are 

 usually carried about by the female, attached to her ab- 

 dominal swimming-legs, until they are hatched. 



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