124 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lie 



appears closely related to C. treitlii because of its very long snout, its 

 bony interorbital width contained twice or more in the snout length, 

 its relatively slender caudal peduncle, and its color pattern. The obvi- 

 ous differences between C. treitlii and C. semiaquilus are the imbricated 

 bony plates on the belly and thorax of the latter (the former has 

 prickles only), a much longer pectoral spine in C. semiaquilus (see 

 table 1 for comparison), a banded caudal fin in C. semiaquilus (caudal 

 bands are absent in C. treitlii), and fauiy consistent differences in caudal 

 peduncle depth between the two species. The profUe of the snout 

 and dorsal part of the head is consistently different in C. treitlii and 

 C. semiaquilus. Corydoras treitlii has the caudal peduncle depth 57.0 

 to 62.1 % of the snout length while in C. semiaquilus it is 48.9 to 50.8%. 



Corydoras cervinus differs from C. semiaquilus in lacldng caudal fin 

 bars, in having larger spinules on the pectoral fin spine, and apparently 

 in lacking belly scutes. Rossel (1962) records the caudal peduncle 

 depth for C. cervinus as 7 times in the standard length. In C semi- 

 aquilus it is 8.6 to 8.9 times in the standard length. 



Of the other known species with an interorbital contained twice or 

 more in the snout, Corydoras fowleri, 2.2 (42.3%) in snout length, is 

 very much like C. semiaquilus in the possession of imbricated thoracic 

 and abdominal scutes and a somewhat similar color pattern. How- 

 ever, these two species differ widely with regard to several proportions. 

 First, C fowleri has a much shorter snout (about 24% of body length 

 without head). Second, the head length of C. fowleri is 26.6% and 

 that of C. semiaquilus is 32.9 and 33.2% of the standard length. Third, 

 the eye of C. fowleri is proportionately smaller, being 6.1%, while that 

 of C. semiaquilus is 6.6 to 7.4% of the standard length. Fourth and 

 finally, the dorsal fin is placed farther anteriorly in C. fowleri, its pre- 

 dorsal length being 66.5% while that of C. semiaquilus is 85.2 to 85.5% 

 of the distance between the origin of the dorsal fin and the caudal fin 

 base. The color patterns of C. fowleri and C. semiaquilus actually 

 may be quite similar; however, that of C. fowleri appears faded and, 

 therefore, accurate comparisons cannot be made. 



Another species, Corydoras pastazensis Weitzman (1963), is very 

 closely related to C. treitlii and on the basis of specimens at hand, may 

 be distinguished from C. semiaquilus by the following characters: 

 C. semiaquilus has a body depth of 33.5% of the standard length while 

 that of C. pastazensis is 36.4 to 37.1%. Body depth, being measured 

 from the ventral border of the posterior coracoid process to the dorsal 

 fin origin, is a stable measurement in Corydoras, little affected by the 

 state of nutrition. Caudal peduncle depth of C. semiaquilus is 48.9 

 to 50.8% in the snout length while it is 65.2 to 66.4% in C. pastazensis. 

 Corydoras pastazensis lacks the dark color pattern in the upper body 

 scutes present in C. semiaquilus and lacks the marbled markings on 

 the snout. 



