108 BRITISH PARASITIC COPEPODA. 



captured near Barrow-in-Furness, Lancashire (A. 



Scott). 



The structure of the mouth-organs of Dichelestium, and 

 especially of the mandibles, shows a somewhat close relation- 

 ship with the Caligidae. The parasite seems to be peculiar 

 to the sturgeon, and to have a distribution coextensive with 

 that of the fish. 



Genus 20. ANTHOSOMA Leach, 1816. 



Cephalothorax of considerable size, in the form of a 

 narrow ovoid buckler having attached to it near the 

 mouth a pair of large foot-jaws armed with strong- 

 hooks. Genital segment furnished with elytraform 

 appendages. Thoracic feet, three pairs, all folia- 

 ceous. 



The two sexes are somewhat similar except that, 

 in the female, the genital segment and abdomen are 

 almost entirely concealed by the elytraform append- 

 ages, but are more or less exposed in the male. 



Anthosoma crassum ( Abildgaard) . 

 (Plate XXIII, figs. 5, 6.) 



1794. Caligus crassus Abildg. (1) vol. iii, p. 54, pi. v, figs. 1-3. 

 1816. Caligus imbricatus Risso. Hist. nat. Crust, des Environs de 

 Nice, p. 162, 'pi. iii, fig. 13. 



1816. Anthosoma smithii Leach. (74) p. 406, pi. xx, fig. 1. 



1838. Anthosoma smithii Kroyer. (70) vol. i, p. 295, pi. ii, figs. 2 & 2a. 



1S50. Anthosoma smithii Baird. (4) p. 296, pi. xxxiii, fig. !. 



1861. Anthosoma crassum Stp. & Ltk. (<?). (127) p. 397, pi. xxii, fig. 24. 



1905. Anthosoma crassum T. Scott. (116) p. 112, pi. v, figs. 15 & 16. 



1906. Anthosoma crassum Norman & T. Scott. (88) p. 214. 



Female. Tolerably elongated, and, when seen from 



above, ovate in general outline but narrowed in front. 

 The head and a considerable portion of the thorax 

 covered by a brownish-coloured horny shield which 

 gradually expands towards the posterior end, and the 

 junction of the thorax with the head marked by an 

 obscure constriction. The remaining portion of the 

 thorax, and also the abdomen and caudal rami, covered 



