800 MR W. T. CALMAN ON 



fig. 16), and on his account alone the following remarks are based. In general shape 

 Acanthotelson resembles the two genera which we have considered above, but the body 

 appears to have been somewhat flattened dorso-ventrally. The head (fig. 16a) is stated 

 by Packard to consist of two segments, but he continues : — " The second segment is 

 distinctly separated by an impressed line from the first, but there is not a true 

 articulation between them, so that the first and second cephalic segments may be said 

 to be consolidated, and to represent the carapace of the Schizopoda." This account 

 corresponds very closely indeed with the condition which we have described in 

 Anaspides, although, as the line in question is not shown in the lateral view, we do 

 not know whether its direction corresponds to that of the cervical groove in the last- 

 named form. Packard describes the second segment as having " on each side a low, 

 boss-like swelling, situated obliquely and prolonged in an oblique direction to the 

 anterior outer edge." It is not impossible that the structure here referred to may 

 represent the quadrilateral area which in Anaspides is cut off from the side of the 

 cephalic region behind the cervical groove. 



The eyes of Acanthotelson are unknown. The antennules have a three-jointed 

 peduncle which carries two flagella. The peduncle of the antennae is also three- 

 jointed, and carries a moderately long flagellum. No antennal scales are shown in the 

 figures, but traces of them are said to have been present, and in an allied form, placed 

 by Packard in a separate genus, Belotelson, the antennal scales are said to be large, 

 " resembling those of the Macrura." 



Seven pairs of thoracic limbs are preserved, the first of these being very large, and 

 armed with stout spines. The second pair are slightly enlarged, the following five pairs 

 more slender and uniform in appearance. None of the thoracic limbs, so far as seen, 

 are specialised as maxillipeds, and it is on this account, we presume, that Packard 

 refers to them as " Schizopod-like," for no exopodites appear to have been observed. 



The first five pairs of abdominal appendages in Acanthotelson are well-developed 

 swimmerets, biramous, the exopodite being "lanceolate oval." Packard states that 

 they resemble the corresponding appendages of Squilla, but elsewhere he states that 

 they bear " a general resemblance to those of the Schizopoda." 



The tail-fan is remarkable for the slender form of both branches of the uropods, as 

 well as of the telson. 



It will be seen from the above account that Acanthotelson resembles considerably 

 the other two fossil forms which we have already considered. The spined raptorial 

 limbs recall those of Gampsonyx, from which, indeed, the present form is mainly sepa- 

 rated by the slender uropods and telson, and by the apparent absence of exopods from 

 the thoracic limbs. We find no further hints of special affinity with Anaspides, save, 

 perhaps, in the structure of the cephalic region, Packard's description of which applies 

 almost exactly to Anaspides. 



Packard's views as to the affinities of the above-mentioned genera are as follows : — 



