530 James Carter — On a Neio Fossil Crustacean. 



Orithopsis, from the apparent aiSaity to the recent Oriihyia. I 

 dedicate the species to the Eev. T. G. Bonney, of St. John's College, 

 Cambridge, whose active interest in the advancement of geological 

 science is attested by his frequent and valuable communications to 

 this and to other scientific journals. 



In general form this species has so great a resemblance to Necro- 

 carcinus tricarinatus, as at first sight to suggest the probability that 

 the difference may result from better preservation than usual. Closer 

 examination, however, shows that the two species are really distinct, 

 and that the modification of character cannot be attributed to 

 attrition or any other accidental cause. Most of the fossils from the 

 Cambridge Greensand are more or less worn, and the degree to 

 which this has occurred may be determined by comparing them with 

 specimens from other localities. The distinctness of the two forms 

 would, moreover, seem to be conclusively proved by the occurrence 

 of both of them in the same " gisement " — the Gault of Folkestone, 

 as I recently discovered am.ong the series of fossils from that locality 

 in the Woodwardian Museum, several specimens of N. tricarinatus, 

 precisely identical in character with the Cambridge and Wiltshire 

 forms. A careful examination of a series of some fifty specimens 

 convinces me that N. tricarinatus is a good species, and that, so far 

 as its details are known, it is properly classified with N. Woodwardit 

 and iV^, BecTiei. 



Orithopsis differs from all the species of Necrocarcinus by the con- 

 formation of the rostrum and of the orbital regions, as also by the 

 greater development of the spines of the antero-lateral margin. 

 These characters can scarcely be regarded as of mere specific value, 

 inasmuch as they are modifications of normal and typical points of 

 structure, and therefore have a morphological signification of such 

 importance as to warrant generic interpretation in classification. It 

 is almost impossible to assign the zoological affinities of the genus 

 with any. precision, as the structure of the mouth, abdomen, and 

 limbs is unknown, and consequently we have no knowledge of the 

 important functions of nutrition or locomotion. So far, however, as 

 the characters of the carapace will indicate, the affinity, as Mr. 

 "Woodward has remarked, is rather with the Portunidce than with 

 the Corystidce. The orbito-frontal characters are very similar to 

 those of Orithyia ; but the armature of the antero-lateral margin — 

 especially the well-developed metabranchial spine — approximates 

 Matuta. The zoological position of Orithopsis would appear to be 

 between these two genera. 



The physiological signification of that remarkable character — the 

 carination of the metabranchial lobes — has yet to be determined; 

 but that it cannot be regai-ded as of specific value only is demon- 

 strated by its occurrence, either as a ridge, or as a row of tubercles, 

 in several other London-clay genera — Portunites, Campylostoma, 

 Bhachiosoma, etc. 



It is woithy of observation that in Oritlwpsis the marginal arma- 

 ture is well developed, but the large dorsal tubercles are almost 

 obsolete ; in Necrocarcinus, however, the reverse occurs — the dorsal 



I 



