BRITISH FOSSILS. 27 



female there are no other abdominal limbs, and in the male such 

 as exist are few and rudimentary. 



Of the appendages, the eye is median, sessile, and not easily made 

 out in spirit specimens ; there are a pair of antennules, a pair of 

 antennae and of mandibles, two pairs of maxillae, and eight pairs 

 of thoracic appendages ; there is a a small labrum and a bifid metas- 

 toma ; but these parts have too little resemblance to any of the 

 organs of Pterygotus to need description in this place. 



The most interesting feature about this crustacean in reference to 

 the present inquiry, however, is the ornamentation with which the 

 body and many of the appendages are covered. The surface of the 

 integument appears in many parts irregularly reticulated, but 

 elsewhere the reticulations assumes the form of a regular squamous 

 sculpture, singularly like that upon Pterygotus, but on a very much 

 smaller scale. 



The general form of the body and the paucity of abdominal 

 members, combined with the peculiar sculpture exhibited by the 

 Diastylidce, attracted my attention strongly when, on a former 

 occasion,* I endeavoured to trace the affinities of Pterygotus. 

 Following the line of inquiry thus suggested, I pointed out that in 

 many Schizopoda and Stomapoda, such as Mysis, Phyllosoma, and 

 Erichthys, either the abdominal or some of the posterior thoracic 

 members, or both, became abortive, and that in the larval con- 

 dition of some Podophthalmia, even the sixth pair of abdominal 

 appendages remains undeveloped, and the abdomen is wholly devoid 

 of limbs. In the larval Brachyura or Zoece all the appendages but 

 the gnathites and antennae are rudimentary, and the long palpiform 

 maxillipedes are (in addition to the abdomen) the only organs of pro- 

 pulsion. The larval lobster (before hatching) is similarly deprived 

 of abdominal appendages, it possesses a disproportionately large 

 labrum, and a metastoma, which is only slightly emarginate an- 

 teriorly, and very large in proportion to the other buccal organs, as 

 compared with its adult state. 



In the paper referred to, I laid considerable stress upon the 

 analogies, w^hich, from what has been said, may be readily enough 

 apprehended, between Pterygotus and the Diastylidce and larval 

 Podophthalmia. Renewed examination of the specimens and of 

 the far more extensive materials which have since presented them- 

 selves, aided by a careful investigation of the characters of the 

 recent Copepoda has shown me, however, that at least as strong a 

 * Quarterly Journal of Geological Science, vol. xii. 1855. 



