208 ELOPIFORM FISHES 



both hypohyals) runs through the lower hypohyal only, before piercing the cerato- 

 hyal to emerge on the dorsal surface of that bone at the bottom of a prominent groove. 

 The afferent mandibular artery of Albula is contained within the anterior ceratohyal 

 and never passes through a hypohyal. 



The paired fins, girdles, median fins and preural vertebral column of albuloids are 

 very similar to those of other Elopiformes, retaining such characters as pelvic splint 

 bones, autogenous neural and haemal arches and parapophyses, and both epipleural 

 and epineural intermuscular bones. In keeping with the rounded trunk the pleural 

 ribs tend to be short, incompletely encircling the body cavity. 



Apart from the primitive caudal skeleton of 0. lewesiensis (which differs from Elops 

 only in possibly having a fourth uroneural) the albuloid tail is distinctive. There 

 are only two uroneurals, the first of which is large and extends to the first preural 

 centrum (in Istieus it just covers the second preural centrum). The second uroneural 

 extends considerably beyond the distal tip of the first while in the Pterothrissidae 

 the proximal end of the second uroneural lies well above the second ural centrum. 

 There are six hypurals, one less than in elopoids. The bases of the inner fin-rays of 

 each caudal lobe are unexpanded, unlike many primitive teleosts, including elopoids. 

 There are many basal fulcra above and below the principal rays, and fringing fulcra 

 are retained in Lebonichthys. There are minor details in which the caudal skeleton 

 of the albulids differs from the pterothrissids and these are mentioned in the discussion 

 of those families. 



The similarity in neurocranial architecture between the Osmeroididae on the one 

 hand and the Albulidae and Pterothrissidae on the other is held to be of paramount 

 importance and has led to the inclusion of the Osmeroididae within the Albuloidei. 

 The more advanced osmeroidids show trends in other cranial bones which are 

 decidedly albuloid. 



The differences between the osmeroidids and other albuloids are essentially those 

 in which the former family is primitive. These primitive features (with respect to 

 the other albuloids) include : a terminal mouth ; the simple maxilla, with a distinct 

 palatine head and forming a substantial portion of the functional jaw ; the presence 

 of two supramaxillae ; the dentition ; the sensory canal system, which is never 

 cavernous although it may be slightly enlarged ; the ornamented cranial bones ; and 

 the caudal skeleton (at least in 0. lewesiensis) which has more than two uroneurals 

 and in which the bases of the inner rays are expanded. 



Osmeroides is the type osmeroidid genus and contains species known from the Albian 

 to Coniacian of Europe and possibly Japan (Yabe & Okada 1930). 0. lewesiensis 

 appears to be the most primitive species, with the closely related 0. levis and the more 

 distant 0. latifrons as derivatives. Of the three species, 0. latifrons appears closest 

 to the ancestry of both the Albulidae and Pterothrissidae. 



The great similarity between the Albulidae and Pterothrissidae suggests that they 

 were derived from a common ancestor. Important similarities have been men- 

 tioned above but may be summarized as the following : snout elongated, mouth 

 inferior ; premaxilla with fine, needle-like teeth bearing a sensory canal and forming 

 most of the upper jaw margin ; hyopalatine series with a long palatine, an ectoptery- 

 goid process and a hyomandibular-metapterygoid foramen ; branchial arches with 



