40 Description of Genera and Species. 



tight upon the middle joints. The tail is at the same time gentl}- Hexed, so that in spile 

 of the applanation the dead animal comes to rest on its side and the fossil ones 

 become thus embedded, and it is in this position that the more elongated of the fossil 

 forms are found. The arrangement for the overlapping of the epimera is so complete 

 that the curves formed by their edges, when the tail is thus flexed, remind one of those 

 made by the adjustable iris diaphragm of some optical instruments. 



To such large forms some special breathing organs would be a necessity, and from 

 certain indications, seen in some of the forms, they appear to have been podobranchiate 

 like their congeners the Lophogastrids and Anaspidians. The females appear to have 

 borne brood pouches on the last trunk segment. 



All the remains belonging to this genus have been found associated with those of 

 marine or rather estuarine forms of animal life, mingled with land plants and with such 

 air-breathers as scorpions and gaily worms, showhig conclusively that they were not 

 deep-water forms. 



Perimecturus PAiiKi (B. N. Peach). PL V., figs. 1-5. 



1882. Anthrapakemon parki B. N. Peach, Trans. Pioy. Soc. Edin., vol. xxx, 

 p. 78, pi. ix., figs. 4-4g. 



General Remarks. — This species was originally described by me under the belief 

 that it was the remains of a macrurous Decopod, a position rxO longer tenable. Viewed 

 iu the light obtained from the .study of the recent Lophogastridse and Anaspides, which 

 was not then possible, and from the study of the well preserved remains of TealUocaris 

 and Anthrap>alcemon afforded by the present Survey collection, it can no longer reman i 

 in the genus Anthrapalamon., nor can it be looked upon as a Lophogastrid, but must 

 take its place beside the other well marked species of the present genus. A consider- 

 able amount of new material is now available, making it necessary that some additions 

 to the original descriptions should be here given. Fig. 1 shows one of the largest 

 specimens yet obtained, natural size, which is over 150 mm., or about (i inches long. 

 The massive tail characteristic of the genus, with the almost parallel sides equally so of 

 the species, are well seen, as well as the details of the tail fan. The new features afforded 

 by the present specimen are that the last five or six trunk segments are complete rings 

 with closed-in dorsal parts, and that they are free and only loosely attached, so that 

 tlie word " Endophragmal " system, used in the orignal description of the species, is 

 quite a misnomer. The size and form of this tail, with its pecular telson, uropods, and 

 the free trunk segments, are strongly suggestive of affinities with the S(|uillids (pi. vii.. 



