162 PROCEEDINGS OF THE NATIONAL MUSEUM vol. in 



Scobinomus serratus Looniis 



Figure 12 

 Scobinomus serratus Loomis, 1953, p. 420, figs. 13-17. 



Holotype: Male, USNM 2091, from 14 miles north of Ensenada, 

 Baja California, Mexico, collected on January 7, 1925, by O. F. Cook. 



Diagnosis: A small arinolid having the characters of the genus as 

 discussed above, and specifically identifiable by the shape of the 

 male gonopods. 



Description: The detailed original description given by Loomis 

 cannot be improved upon except as regards the formation of the 

 gonopods. Study of a male paratype has provided the information 

 following, and it should be mentioned at this point that the gonopods 

 were cleaned of all adherent muscle tissue and mounted in glycerine 

 to facilitate examination with considerable magnification. This tech- 

 nique, we feel, provides a more detailed picture of structure than can 

 be gained from the study of untreated parts. 



Anterior gonopods in this form (fig. 12a) are similar to those of the 

 species of Arinolus in most respects. The sternite is nearly trans- 

 verse, and is enlarged laterally near the origin of the sternal apodemes. 

 On the caudal side the sternal extension reaches only about halfway 

 to the mesial end of the coxite, a detail that is apparently constant 

 in the subfamily. The coxites are large, and mesially are produced 

 toward the sternite, a matter of structural necessity since there is no 

 median vinculum to keep them separate. Each coxite is impressed 

 on its anterior surface with a distinct oblique vertical groove that 

 merges distally into several shorter perpendicular grooves. 



Owing to the form of the coxites, there is little intersegmental 

 membrane in the make-up of the anterior gonopods; what is present is 

 largely in the form of a pair of ligulate processes extending distad 

 between the coxites. In untreated material these processes are so 

 closely appressed as to appear as a single structure. There is some 

 membrane in the form of transverse folds along the upper edge of the 

 sternite, the material forming an enlargement near the middle of the 

 basal edge of each coxite. In caudal aspect (fig. 12,6) there is Uttle 

 of particular mterest to be seen except for a small internally projecting 

 process near the base of the sternal apodeme, a development not 

 observed in any other species. 



The posterior gonopod (fig. 12,c) as seen m caudal aspect has the 

 usual long apodeme connected about a thu-d of the length from the 

 mesial end of the coxite. The latter takes the form of a slender rod, 

 near the lateral end, enlarging mesially and then reflexed laterad and 

 extending behind the telopodite. There is considerable consolidation 

 of the gonopod, with little indication of the two distinct elements 



